Anyone worth leveling besides 4* Thor and Fury?

Marvel Puzzle Quest MPQ Tips and Guides
1

As the post says:

I have most 3*s cover-maxed,

209 XF, 166 Daken, 166Thor, 166Patch, 166Blade, 166Rocket, 166Sentry, 166Punisher, 166BlackPanther, 166CapAmerica, 166Deadpool, 166Magneto, 166Daredevil.

Many others at appropriate levels for my play style: Hood at 130, Loki at 102, etc.

I only shield hop to get the 1000 rewards, so HP right now is over 10,000
I haven’t bothered leveling anyone this month so ISO is nearly 500,000

Do I have any reason to save ISO for leveling anyone other than Fury (who I have at 5/5/2 level 70)?
Do I have any reason not to spend 5,000 HP to take Thor to 3/2/5 and level her?

What am I going to do…buy Cyclops covers? He is nice but spending HP on 3s feels like a waste.
The only 3s I ever consider leveling are Mystique (85 right now, 2/5/5) and Cage (102 5/3/2)

2

If you have Xforce/4thor, there is no point in leveling anyone else.

I would just save it all for the next powerhouse 4*.

3

I think you should be focusing on your 4* characters, yes.

The only other 3* I might consider is Doom, for his great purple power.
Mystique is kind of broken in PVE with MNMags but you probably have enough PVE options already.