I think we have to come to terms that the show cares little about evolution's when it comes to actual strength. The difference with Sun and Moon compared to say Best Wishes (as an example) is that Ash actively is seen training even if only briefly during opening scenes of a majority of episodes. Hence why Rowlet is actually on par with Torrecat's and Lycanroc's power despite its lack of evolving. I'm more concerned by the fact Ash's last 2 Pokemon, if he even gets any at this point, are gonna get the Gible and Snorunt treatment.
I think what ultimately pollutes our minds is the games themselves pretty much saying that if we want to be successful, we need to evolve our Pokemon to make them stronger. That and probably our bias towards certain Pokemon's evolution forms. I myself have made it known plenty of times that Decidueye is easily one of my all time favs of Gen 7 when it comes to starter evolved forms. I'm disappointed sure, but it's not like Rowlet is gonna get treated poorly, it has a very solid battle record up to this point.
You are right in that Rowlet is NOT going to be treated badly, it's already out performed Snivy and Oshawott in many different ways.
I feel like me, the writers are purpose and intentionally preventing Ash from getting new Pokemon that I think he deserves, and that's kind of the issue, isn't it. That literally the only reason to keep a Pokemon unevolved is because of aesthetic reasons. It's literally the worst reason to deprive someone of a Pokemon.
Sure, to some extend I'll buy a Pokemon's desire to not evolve, but with Rowlet, and the everstone it looks VERY forced that the argument really doesn't apply all that much. It's just so incredibly obviously forced that they don't want Rowlet to evolve, one for there being a random everstone, conveniently in the middle of the forest, that Rowlet conveniently likes the "taste" of it, all while using it specifically for Seed Bomb, because somehow a specific grass type Pokemon can use its own grass type energies to pull it off.
It's so forced that it hurts so much that they didn't even try to hide it, or attempt to make it natural (even though it still wouldn't be natural). It felt like middle finger to both certain fans of evolved Pokemon while to Ash as well, especially since they had to write that Ash was interested in having Rowlet evolve, like really? At least have Ash pretend it doesn't matter if Rowlet evolves or not, instead of freaking out that it will never evolve, and then just have him figuratively shrug his shoulders.
Not to mention conveniently giving Hau a Dartrix just to justify Ash not getting one.
And I don't even want to get into the garbage that was Poipole, and what's likely to be Eevee, and then there shoving Zeraora instead of actually attempting to fix his team, it's clear to me (and I don't care if I'm wrong, because I just don't see how I could be) but they insist on screwing Ash's team over, either by depriving him Pokemon, figuratively (Decidueye) or literally (Poipole/potential Eevee or even just something). I have just lost all faith in Ash's team ever being redeemable, I just don't know if I care if Ash gets Wimpod in the January and get Golisopod with a bug type Z-move, I just don't know if I could even care at this point.
Because they had to focus on (well at least what I perceive) to be crap first and not patching up his team, after the whole Poipole nonsense, and then forcing Rowlet not to evolve. Eevee getting needless amounts of screentime even though it's not likely to be Ash's at this point, and the whole RotomDex annoyance, and now after all this, is Zeraora, and then Brock and Misty, it's like they just don't care at all.
I honestly don't expect any Pokemon league at the end of all this. Because this is not the makings or series that's leading to a Pokemon league without stupidly using Pokemon reserves because they couldn't be bothered to actually give him actual new Pokemon.
I mean Ash has one more grand trial left, what in the hell is Ash's next Z-crystal, because Torracat STILL doesn't have its own Z-crystal. I just don't even know what the hell they are doing and I honestly don't think they know either.
I just pray 8th generation will be a lot better than this, this isn't 5th generation bad but its getting close, but at least 5th generation had some things going for it, that 7th generation is just going to fail at.
But that's just my opinion, I fully expect people to see things differently.