Grand Challenge aren't bot teams. It's players teams, similar to crusade...
I have faced guild members there and it just represents the current meta.
TF, IE, CMDR, Mani, HN, DV are just most used heroes in top rankings... Then also CA, Griffin, DM now, SH...
I can see in Arena and so also in GC the variations become more a bit now.
Top players have focused on those first and now have time to invest in others...
That's said, I still agree some over works on older heroes would be good.
But also said, this needs to be well balanced
Otherwise it will end up same. Let's say PK becomes superstrong.. Then everyone will get and use him.
Some actual heroes become really good only from red or even red1 on... DM is getting popular as she also doing great in Arena at r1.
Against some setups Bear Warrior is great.... Lightbringer was a joke before o2, SH wasn't really much used, etc, etc..
What I just say: many players just follow the meta, ignoring other heroes, but I think some could be great at red/r1 already now.
Although, as said, in certain cases over works would be great, if not really good balanced (and that's not really the strength of ucool) it will end up in a few getting really good, many people concentrate on those again and all use similar teams again.
And might complain why (just for example) professional killer suddenly is so strong and they have to gear him up from maybe purple (if even).
So basically same as getting a brand new hero... (except you might have him 5* already)