Actually, all characters scale identically now (for attack scaling) - at the scaling rate of a 4*. Check the R69 patch notes. Juggernaut was the main reason this was fixed. He’s tremendously powerful to begin with, and when he was scaled at the higher 1* rate over hundreds of levels, he became ridiculous. Now he’s only obtusely powerful when scaled.
The issue I’m raising is that if you make Ares a 3*, his ‘base’ damage is going to be significantly higher than the 2* Ares – and even though the scaling is over fewer levels than the 2*'s scaling, the higher starting point leads to a higher endpoint.
If you assume that the scaling rate is 1% per level (I don’t know the actual %, this is just for illustration), then a max 1* raised to level 200 does 491% more damage, a max 2* raised to 200 does 287% more damage, and a max 3* raised to 200 does 140% more damage.
Juggs lv 40 does 1100 damage for 5 red with Headbutt. So under this example, at level 200 he’d do 5405 damage.
Ares is tricky, because he’s variable damage based on how many green you have. But the minimum 6-green trigger at 94 does 1242 damage. Scaled to 200, that’s 3566 damage.
3* characters, so far, do AT LEAST 2x the damage of 2* equivalents. Look at LThor vs. Thor, or the two Torches. By that metric, Hypothetical 3* Ares would do 400 damage per green. Keep the trigger at 6, and that’s 2400 “base” damage. Which, under this, would scale at 200 to 3484. And that’s the minimum.
Edit: and if you run the numbers further, you’ll see that 2* and 3* will be pretty much the same when scaled up, or at least within a couple of percentage points, if 3* damage is 2x 2* damage.
Juggernaut is even more stupidly powerful, because his damage at 50 is proportionately HUGE compared to damage by 2*s at 94, so scaling him gives you 44 extra levels of compound interest on a huge base.
So while it’s admittedly not as bad as I first thought… I still don’t think we need a 3* Ares, thank you very much. 
tl;dr Juggy’s ridiculous.
Edit: I caught a math error here. Will fix and update…
Edit: Fixed. Of course it ultimately ruined my original point. Stupid facts! Stupid Smarch weather!