I kind of like it. They are basically the old ex pokemon (have to be evolved). Their hp is kind of high tbh but I can't judge it until they reveal other non-GX pokemon.
How it is is it not playable? No offense, just curious why you came to this conclusion. This dude hit freaking hard with Regirock + Strong Energy. Not to mention it has 200 HP and only a Stage 1. I will probably mix Slowking with Lycanrock to wreck havoc.
They can marry when they're older. Oh wait, who am I kidding? They don't age. #4ver10
Anyway, Serena will end up just like Misty and the rest. Been like this since forever.