Imo, its your fault, unless you're 5 meters from the ground and outta nowhere u get slammed into it, and your not holding space. Sorry, but the fact is you shouldnt go near walls or the floor when you're low on ki, if you do you better be trying to walljump or jump and teleport. If you have enough ki you can hold space and you're probably gonna get out of it before its even formed. So due to lack of ki management and inability to recognise dangers, i say its perfectly your fault if you get slammed into something and you cant get up. That is afterall why being immobilisation was implemented, to give you a disadvantage. Scince thats when renzoku was most commonly used in the show, it stands to reason that thats how it should be in the game. The only instance where it isnt your fault is if you're thrown/hit rolling along the floor, however I believe in 1.3 there will be recovery measures in such occasion like skiding instead of rolling.
Thinking about it a bit, i think generic balls creating a kiblob when hit into a map surface could be quite a good idea... then you can add to it with kiblasts if you want to, or splode it with generic beam. I dunno, atm when somebody gets immobilised, kiblasts have just about enough time for you to shoot 3-4 kiblasts to create a ball then shoot of a generic ball for it to explode, it also requires a knowledge of the timing, its not just garenteed. I think its quite deserved most of the time, but i agree the damage should be toned down.
Edit: to ravendust
I dont see how standing in a bubble of intense exploding ki isnt going to hurt you... I mean really, they didnt do it cuz it looked cool :x (at least i dont think so) because they did stay there for a good 10-20 seconds sometimes depending on how much time everyone was saying "omg ive never seen a fight like this, they're so powerful!"