Not having seen it, you wouldn't realise that it's almost ruining the show. It's uninteresting time wasting that's robbing the main cast of time they should have devoted to themselves.
It's not like Amuro showing up and being a secondary character helping out, they've fractured the show completely and run them almost like a second main cast running a completely separate plotline from the main one. It's awful.
True I haven't seen it, but I also don't think they should abandon the original cast, as there were still some large mysteries surrounding Kira at the very least. Maybe it's not the best idea to introduce a new group of characters, and then push them off to the side, but there's still half the show to bring things to a full head.