While we're on this topic, anybody else sympathize with the Gym Challenger who's an old man and reveals himself to be a Steel-type specialist? I found it interesting they included him into the game to show that there is no age ceiling for the Gym Challenge despite most of the challengers being young. This is an issue I sometimes see pop up, especially in regards to sports, in which people are shunned if they engage in particular hobbies past a certain age. For instance, there is a soccer program near where I live whose members are middle-aged to elderly, I guess the opposite to a youth program. They get together and play noncompetitive games weekly at a nearby field. They're made of people who just simply like playing soccer. To my knowledge, it's the only such program in the area. All of the other ones are oriented toward children and young adults. This NPC shows that, if you show promise, you can be endorsed, no matter how old you are.
This elderly NPC is also shown to have obtained seven badges before dropping out to Raihan. Raihan says there are less than 10 challengers left by the time you get to battle him, meaning he wound up among the top ten challengers for the season. (Incidentally, this also means, as a Steel-type specialist, he managed to beat Kabu and, in the Sword version, Bea, both of whom should have a major advantage against him.)
Piers is personally opposed to Dynamaxing; he refuses to do it even when a Power Spot is nearby. Of course, his hometown doesn't have a Power Spot either, but we do see he's not too fond of the concept. (And because he battles in a small area without many spectators, he's the closest Galar has to a traditional Gym Leader.)
As for Fire-type specialization in Hoenn, I think it's quite viable. I mean, Team Magma is focused on the type (albeit alongside Ground). It also fits in with the fact that Hoenn is volcanically active and has the warmest climate of all of the regions based on Japan.
You know, I think you just hit the nail on the head about why Opal is so interesting to me. I described why earlier, but I felt like there was still something about her that made her a more appealing character than the other elderly Gym Leaders. It's because, seeing her during the orientation, I thought she was going to be one of those stuffy, snobby types, but it was refreshing to see her be energetic, outgoing, and behaving very much like an eccentric artist.
It's also a weird sight to see someone who's maybe 80 or 90 years old standing out there in a stadium as a celebrity.