Focus on your **'s for now. ***'s take a LONG time to get covers for and level up. I’m still transitioning. At day 121, I have 2 ***'s over 100, 2 ***'s @ 90, and a bunch lower. Even if you get the covers, it’ll take you a long time to get the iso to level them.
My first usable *** (i.e. that was of a level where it made any sense to use them), was around a month ago. A big help has been the awesome alliance I’m in since we regularly rank well, and I’ve put some money into this game. You should know that without a lot of grinding, and/or spending money, the F2P portion of this game more or less stops with the **'s. It’s doable to build a *** team without spending money, but it’ll take you a LONG time and playing the game everyday almost like a second job. It took me about 3 months of playing regularly to finally start getting ***'s that weren’t just sitting there as collectibles in my roster spots.
But in answer to your question, I have run into surpluses and dearths of token pulls. On average it should even out if you keep playing regularly. I’ve gone through extended periods of getting nothing but junk pulls, broken up by a seeming flood of rares. One time I had a week of very good luck and pulled two invisible woman a day or two a part, but that’s rare. I’ve actually been tracking my token pulls, and overall my pulls have been roughly consistent with the published percentage by Demiurge. So bad or good luck only really affects you if you aren’t playing regularly. Over time it should balance out to the published percentages. Which basically means the primary source of getting covers is from winning tournaments, and/or buying them. So you really need to work on building your ** roster to a point where you can begin to compete for *** covers, or buy some cover packs. Generally you shouldn’t buy cover packs though, especially now with no guaranteed rares, unless you need a ton of uncommons as well, and even then they’re expensive. Typically if you’re going to spend any money on covers, you should wait till you have at least 1 cover in the power that you want to upgrade and upgrade it directly, which seems expensive but cheaper than playing the slot machine most likely.
My other comment is that devs seem to be increasingly punishing players for leveling their characters, and especially for building out strong *** rosters, so you may not even want to bother, and stick with **'s. If it makes you feel any better, I had an extremely slow start. I had to play nodes in prologue about 20 times to actually earn anything other than initial reward or 20 iso, and usually it involved my characters wiping each time. If it hadn’t been for pvp token pulls, I’d have probably quit then and there. This game can be fun, but there’s a strong focus on encouraging you to make meaningless, expensive purchases, so it’s probably in your interest not to worry too much about ***'s until you actually have a bunch of them collected, or a strong enough ** roster that you can start winning them, and even then, it may not be in your interest to try to make the transition. If you manage to get ***'s, I’d keep them around for when they’re featured in pve events, but I wouldn’t go nuts worrying about whether you get them or not. At present, the game punishes you for actually using them.