That's a Pokemon that should definitely be a filler episode with a tad bit of James focus like the Chingling episode in DP.
Uh no it isn't lol
Since BW ended and before Ash got Dracovish we spent YEARS without there being a single moment where Ash actually had a full team, it was always 5 Pokemon. Of course people wanted Ash to get more, it was annoying that he didn't seem able to hold a full team anymore! When Ash released or dumped somebody in training that meant we'd get a replacement, Phantump vs Gogoat wars, various SM Pokemon predictions with Jangmo-o being the most prominant prediction.... they never did bring a replacement in and just brought Goodra and Poipole back only to send them away again. That is pretty much it apart from Ash haters going "Hurr Ash is too freaking stupid to catch Zapdos when he beat it!"
And rotation done right but there's a major difference between wanting Ash to own 6-9 Pokemon and Goh getting 100 in a single year. OS was the beginning of the series so it gets a pass, Johto was still finding it's feet and dragged the Kanto starters along before needing to come up with a reason to bench the three. Then comes BW and everyone's surprised when Ash gets a seventh team member, then that surprise quickly turns to annoyance when the team turned out to only have one actual slot in rotation due to Pikachu, Scraggy, and the three starters existing.
Hardly anyone complained about him not catching legendaries, it was the League and him releasing things that people complain about(Rightfully so on Goodra/Poipole's part but apart from XY most of the League complaints weren't justified in the slightest. 'Ash lost to a dummy' man who cares? Sure I'd have preferred seeing Benga or Hugh take him out but what's done is done, there are FAR worse things in BW to complain about. 'Tobias' It felt like a compliment creating a guy like him to make Ash lose, Ash was just that good!
Imagine if Ash HAD a legendary, nobody would be able to accept Ash losing that league(Well maybe some but what I mean is Ash would be extremely ridiculed for that loss). Besides which one was he going to get? The Hoenn/Sinnoh trinity are basically gods, past Pokemon were seemingly banned from his team so the birds/beasts were out, Infernape cancelled Heatran, Regis were Brandon's, be odd to single him out on the lake trio given the whole thing was to signify Ash/Dawn/Brock's importance, BW was basically OS 2.0 where they seemingly tried avoiding Ash being OP(I'm still on the side that says he'd have likely gotten Zekrom had TP actually happened though). XY was the first and currently only region to have zero legendary Pokemon outside of the trinity. SM treated the Tapu like guardians(as they are in the games but you really only saw Koko), it'd paint Ash in a pretty bad light had he tried to catch one. Nebby... yeah, that should have happened. Just keep him as the cute nebula cloud for a longer period and then Ash has a Solgaleo, Ash actually formed a bond with him and everything. It's not a 'OMG so OP' Pokemon like Rayquaza or Zygarde would be. And ever since Ash beat Articuno he proved himself worthy of owning one, Goh didn't. Just threw a ball and hurr de hurr, it caught! I swear the people who defend Goh don't have respect for Ash at all! For years people went 'lol people self insert as Ash' but funny how the tables have turned and people start whimpering and crying foul at the slightest insult hurled Goh's way, even when it's completely justified! People live through Goh lmao
Also people would be FAR more accepting of Goh owning a legendary had Ash owned one first. Look at Melmetal, Ash got it. Mallow bonds with Shaymin, Lillie got Magearna. Nobody cared, you could argue that Lillie got off due to her popularity but as Mallow's seemingly only fan that sure as hell ain't true for her. Most fans just want Ash to own ONE, that's it! I'm one of them, I write fanfic and the one and only one I've ever given him other than Kubfu is a Latias. Wanting Ash to get ONE doesn't excuse Goh getting MULTIPLE or potentially dozens!
Plus catching legendary Pokemon kinda takes away the charm and novelty, especially when XY/SM is where it started to die down. "Oh look, Moltres/Zapdos.... again." "What's a Kyogre doing in Alola?! And who do these poachers think they are? The TRio stand as much a shot at getting it as they do!" "Zapdos again really? You just did that again a few years ago." "Why do Celebi keep kidnapping children? And just how many exist? we've seen one almost every generation!" "Suicune, well at least it's been over 10 years" "Moltres... *sigh* Oh, Infernape's battling it that's a great comeback for bringing in the reserves!" "Wild Regice? Ugh, please don't ignore Brandon for the new Regis..." (Yes, that is a legitimate concern I have at the moment. I know they could just be getting the old ones out of the way so Brandon can use the new ones on his potential 3v3 with Ash but it's still worrying and honestly would be pretty annoying if he DOES show but is excluded from the new Regidrago/elec focus episode). Bad enough they appear like the common Rattatta, you want them treated like them too being caught like one?
The games are more than excused cause you can't honestly expect to say 'Well they didn't play HGSS so they don't deserve Lugia' is fair. It's fairly easy to ignore them outside of Rainbow Rocket's plot, the anime waves them in front of your face and just annoys you when certain ones like Celebi, Kyogre and the Kanto birds(I'll give them a bit of a pass this time since they need to showcase the difference but my point still stands) appear for the 4-10th time and most of the Unova legends/mythicals, Marshadow, Volcarona/Diancie/Hoopa never had episode roles and despite this series supposed to having a 'world tour' vibe going on, we'll still likely not see them.
I'll admit to being a slight hypocrite on hyped for a Zeraora appearance as stuff has implied but we never did get to see one in Ash's world, it was an AU in both circumstances. We never saw Zeraora from the main earth and it could be a good candidate for a second Electric type, assuming Toxel/Toxtricity doesn't break the status quo first.
Hopp'll likely be the one with Rillaboom or rather the one to debut it, I'm honestly surprised that Wooloo hasn't joined the cast yet given how popular it is. Though I also thought Ash would have beaten at least one of the Galar gym leaders by now...
I guess it could happen in Tundra but there probably won't be time if they stuff the Mew Squad and Regice into a single episode rather than splitting it up. I really hope Ash starts battling the gym leaders for the PWC soon cause that honestly feels like the only way we'll actually get to see Galar Pokemon. Hope that female is Nessa...