Yeah, you get a new batch once every few years, and nothing gets rotated out.
Apparently, there were some tournament organizers who tried doing the video game side events on their own, but they didn't know enough about it to understand what was going on in the matches and, more importantly, check to see that nobody has cheated. Every time I run it, I get a lot of questions about how stuff works in Pokémon battling; I realized that you do indeed need a comprehensive knowledge even if you're not going to battle at all the whole day.
And yeah, I noticed that Ferrothorn is present in rain teams AND sun teams, and that alone tells you that Ferrothorn is adaptable. It's one of the few Pokémon I see frequently in every battling environment (though it's somewhat rarer in rotation battles). You won't see Skarmory in any type of battling besides single, for instance, because in the others, there'll be a special attacker ready to attack 99% of the time.
Another big difference I noticed is that in the TCG, your Pokémon carry no secrets. The moment you bring it up, your opponent knows exactly what it does, and even if they've never seen your deck before, they can have an idea of what you're going to do. In the video games, a key part of performing well is to keep as much hidden as possible. Your opponent can't be certain of what you're going to do until you do it.