Hello,
A feature that i think would be nice would be an instant leveling up button. Basically you press it and your toon goes from say 70 to 71 instantly. No longer do you have to wait for a bar to fill for 3-7 seconds or however long it takes in the current format.
And one that let’s you use all of your remaining iso.
Let us combine both of your suggestions into one shall we? Three buttons. First is instant 1 level. Second is instant as many levels as you can afford. Third is to max out insert hero/villain here.
and fourth give me back the iso I wasted on the last featured 2 * 
Why is this not a thing?