It’s definitely harder than ever. Back in my 2* days (season 3) when the brackets of death weren’t nearly as frequent and the 3x166 wall was still at 700 points, a 650-750 score would almost always guarantee top 25. Nowadays even just on the climb up you can clearly see those kind of scores are going to stand no chance of top 50 let alone top 25.
I never made near Top 25 with my 
roster…
I do place in the Top 100 most of the time with somewhere around 500 to 600. My strategy is to begin the PvP early get up as high as the maxed
wall & then go up / down a few times between the wall & the maxed
level which seems to keep me around the Top 80 to 100 in the end so that works for me. 
My alliance is also consistently placing in the Top 100 so I usually score 2
covers per PvP which helps a lot for my roster development…but it is still a marathon of an achievement to make the transition. Technically, after 2 seasons (this one being the one when I maxed out a few
characters a third of the way into it), I did not even begin my transition as I don’t have any
over level 90. It is absolutely a slow process even in my fortunate case of being in a Top 100 alliance…
Just my 2 cents…but a suggestion to at least help out a little would be to have different colours of cover for placing Top 100 individually & Top 100 alliance…at least different powers would be available on my
characters which would maybe make them a little more usable. They do seem to switch the colours around every time the PvP runs them as a reward but still it would be good (even if it is just a psychological boost) to score different ones every time instead of having to play the events 3 times over I don’t know how many seasons before you get a fully activated character.
Hang in there maxed
rosters out there…it will take a lot a patience but we can get there…I know that I will eventually! 
EDIT: Roster slots are also somewhat of a problem for transitioning players I would say…there is so many
characters to keep around just in case you get lucky with one of them. I think that I currently have something like 28 roster slots…but only around 8 usable characters that I actually use in events (2 of them being maxed
heroes) which means that I have around 20
characters at different stages of development but mostly just a few covers (1 to 4 or something)…so it is quite a challenge to manage. I had to drop a number of
covers at one point or another & decide what was more worth keeping. I try to base my choices on the fact that some characters were either weaker or too situational which would not sustain my eventual transition or were too similar to other character powers because I like to try to keep diversity & potential good duos in my roster…
I did also make some personal preference type choices as well just because I like the character better… 
Look at all the “never have done it”. This is why the change to one color rewards was terrible, it’s nearly impossible for the transitioning folks to get the 2nd color (top 25), and if they somehow have gotten lucky (unlucky?) to get five covers in one color they get no progression for that PVP.
On my part, for the PVP, I always use
and
and sometimes replace
with
All of which are maxed at Lvl 94. I have reached Top 25 several times at least 300-350 points. I am also able to reach Top 10 at certain points. What I have observed are these:
- Your ranking depends on your BRACKET
- It depends on the CHARACTER REWARDS (The newer the character, the more players and grinders)
- It also depends on your time frame when playing. When you play when the competition starts - 2 days and more, the easier you get to be attacked and diminish your points. I have played midway the tournament and grind it in the last hours. This really helps secure your ranking especially when you face the MONSTERS in the game - Maxed level
and even
Hopefully, when the End Times Update happens, we will be given a better bracket, better opportunity on winning and better chances of getting even, even we’re at the
land.
So here’s the deal. Most of you who have at least a few mid to high tier fully leveled 2* characters in your roster know that it’s virtually impossible to make top 25 in PvP these days. In the early days that was possible simply because there were a lot fewer players with 3* rosters let alone viable 4* characters.
I myself hit 701 once completely from defensive wins. I was in an odd place where my defensive team was getting pelted right from the mid 200s. I watched my score go up to over 500 in just 45 minutes from defensive wins and losses at which time I decided to shield in the last 3 hours at 484. Now, you’re supposed to be invisible once you shield but so many people had me queued up as a juicy target that I continued to get hit over and over until my score finally reached 701. This was the one and only time I’ve ever hit the top 25 with a 2* team.
Today, if you have only a 2* team, expect to only get to 500 at best without defensive wins. Once you cross 400, you start getting hit frequently and you’ll usually lose more than you gain so it’s best to stay below 400 and only get hit once in a while. To stay at 500 you either have to climb 30 minutes in the tournament or do it early just before the last 3 hours of the tournament and then shield. Difficulty here now is not just climbing but when you approach 400 you will not find high point matches anymore unless it’s up against a level 166 team of which you would not stand a chance with. This happens because most others like you can only reach this far and most quit here so your match points decline as you climb up towards 500. Crossing 450, you start seeing lots of level 166 teams so you have to skip many times to find another 2* team to play against. All this takes a considerable amount of time and at the same time you become a juicy target for those higher tiered teams climbing late. You can reach a point where if there are a lot of people trying to make top 100, you will lose more points than you can gain. Your best bet to get and stay above 500 is do it earlier and shield; you might get a couple of defensive wins within the first 30 minutes of your shield and then get yourself up to around 550.
To answer the real question about 2* transitioning to 3*. Well that’s obviously much more difficult now because you’re not able to place top 25 in PvP hence you’re earning covers at 200% more time. What some may not realize is there is also the dilution of 3*/4* characters as many new ones were introduced since the early days. This makes it far more difficult to get 1 or 2 fully covered 3*. I am at day 134 since I started playing but the game is now over 380 days old. Even from when I started, it was easier to get to a fully covered 3* than it is if you started today. Also the way D3 has adjusted cover rewards in PvP is less favorable than it was before. In the old days, if you and your alliance placed top 100, you would get 2 covers of 2 different colours but now, you get 2 covers of the same colour.
So there’s my 2 cents. BTW, there’s also the viability of 3* rosters of today and 3* rosters of tomorrow (when you get there; things will be different and not as easy as it is today to make higher scores).
This is, what i want to sign first glance. I experienced the same couple weeks ago, when i was trying “to get there” with my 2s.
Second glance, i want to add, that this situation will be even worse, as now, with more and more maxed 4s in the world and more and more decent covered X-Forces out there are not really encouraging the 2*s to get into the top 100, not to speak about top 25…
Boom, bumper.