This part in the game has always bothered me. If Crono can jump several feet onto a dragon tank on a narrow bridge, why can he just jump that small gap in the basement? At least put some lasers in the way.
I really like your way to draw these characters, especially Chrono. He doesn't look so muscular, (as many drawer draws him) and that's why. Ok folks, Chrono IS YOUNG. I bet that no one boy aged 14-20 have really big muscles?
The height of the jump is directly proportional to how badass it would be to complete a jump of that height. There is nothing awesome about crossing ruined platforms in the future, but dragon tanks on bridges in the mountains never had a chance.
I say invisible plot walls, but for the hundreds of times I played Chrono Trigger that whole "jump" thing never crossed my mind once. I just accepted the fact we needed a "key/password" to get through.
This is a common occurance among JRPG protagonists. They can jump several feet either forward or into the air, but they can't cross even the smallest of gaps later on. Well really, I don't think it's that they can't, they simply refuse to! It's like, such a small jump demeans them. They would rather walk around than sully their magnificent jumping legs with suck a paltry obstacle as that.
Meanwhile, all the platformer protagonists are like "WTF"