Yeah, the fact that it can't be destroyed is insane. Rampart barriers are fairly easy to destroy, especially when they are building and they take a few seconds. Gibby's cannot be destroyed and deploy instantly. He is pretty far above other defensive characters. I was thinking about Crypto's EMP too, but if you make only one or two legends able to defeat a Gibby bubble then those legends become mandatory to counter Gibby. Maybe make the shield have a targetable "generator" which can be killed, but it's really small, so it's easy for pros to kill, but more challenging for people at lower skill levels.
Either way, you bring up a good point. His play rate in casual games is very low. Part of that is just people wanting to play more aggro when just having fun, but a part of it is just casual teams not having good communication and teamwork so Gibby is less valuable. Whatever changes should hopefully impact Gibby at pro levels, but not nerf him into the ground at lower levels.