I don't think Ash's companions excelling in their respective fields correlates to them outshining Ash. I honestly think this has become an issue only after the introduction of Goh. In the prior series, since Ash was the protagonist, it was obvious that most of the special captures/popular pokemon would go to him and not his companions which is obviously something important to a lot of people. However, in this series, since Goh is a main protagonist alongside Ash, some of these special pokemon/popular pokemon captures get shared between Ash and him. And also taking into consideration the fact that Goh is a rookie and Ash is a veteran trainer, people tend to get all the more upset when the former is given these prized awesome pokemon which Ash deserves more than him.
The only other way a traveling companion could've technically outshined Ash is if they were also Pokemon Trainers who wanted to take part in the regional leagues or the pwc etc and faired better than Ash. If Goh entered the pwc and comes close to Ash's rank, people would flip. Or if Goh entered the Galar league and ended up winning it (Unless they do something to establish the Galar regional league trainers are significantly inferior to trainers around Ash's rank in the pwc).
So in conclusion, I think people only seem to care if the traveling companion's success in something. makes Ash look bad. In Kalos, Serena technically won the Regional League Alternative of the Pokemon Showcase and went toe to toe with the Kalos Queen who in theory is relative to the regional champion. In other words, This would've been Ash winning the regional league and then losing against Diantha but her success doesn't necessarily make Ash look bad as they both are in completely different fields.