Eh, this reasoning I feel is a bit weird given they did overdone matchups like Ryu vs Jin and Madara vs Aizen, as well as MUs like Mario vs Sonic and Goku VS Superman, that reasoning could have applied to them as well. Also, they could've done some unique stuff to make it stand out cause afaik, I don't think any of the animations used Sword of Hope or Rage. And as for Silver not having enough material, yeah I kinda disagree there since he has a appeared in some games and they could use spin-offs as supplementary material or even IDW since that's closer to the games than Archie is and they did it for Shadow. Even in games like Generations and Forces he still played kind of a role even if he was largely just there. Also, they've used characters with less material before lol. And they're literally using Sauron who has limited screen time iirc. So yeah I find this reasoning a bit weird. I'm not mad by this, just find it weird.
And yeah I hope this means Gohan vs Superboy doesn't happen.