I am a fan of interactables and think they are an important part of the game. For one, they are really something that distinguish IGAU from other fighting games. Second, they add a lot in terms of making IGAU feel more extra-dimensional, really, more interactive. Having stage selection be an important part of strategy was intended. In MK9 you see the same couple maps over and over: do I want the longest map to zone or the shortest map since I rushdown.... It is cool that a character that might have an advantage in a mu on one map has a disadvantage on another.
I do somewhat agree though that non-bombing gadget characters with a jump or jump-down attack seem a little hampered against power characters, then again, there are stages where they can use all the interactables. Are the designers *sure* they amped up the non-bombing gadget characters enough to make up for this obvious disadvantage? Time will tell. I do see a lot of top players with non-power characters, like Batman, Nightwing, Deathstroke, Green Arrow, so it obviously isn't a crippling disadvantage in their opinion to just be gadget.
Also, the hitbox on some interactables does seem a little large. What was it, the Metropolis roof with the hovering robots, at ECT V you could see the characters jump way high out of the way of the explosion, but it still wasn't enough. Even way up in the air, still hit. I'm not wild about having interactables where that is it: if it is thrown at you there is nothing to do. Can't block, can't backdash, can't run, you are just f---ed. At the same time, it was very interesting to watch the play around interactables. You could see a character in the corner who all of a sudden seemed to have an advantage by being in the corner, because of a missile launcher or a pig. You can see terms like "flower pressure" becoming standard. Start on Fortress of Solitude and right away there is metagame going on around that spiked chandelier. To me this dynamism is good, not bad. Just some might need tweaking.
One possible nerf (short of banning them, adjusting damage, or adjusting hitbox) would be to slow the start-up. Particularly for power characters. You want to pick up that massive interactable with an enormous hitbox and damage, and smash it down nearly unblockable, fine, but it is going to take a little longer.
I am all for loser choosing the map.