Couldn't find any mentions of it, but Relicanth is consistently a terrible Pokemon for in-game usage. It almost always comes very late (RSE, ORAS, and USUM, for example) or comes post-game (like Platinum). Even then, in RSE ORAS, and USUM, it has to be stupid rare and have a 5% encounter rate at best. Finally, Relicanth is almost never doing anything that would be worth the hassle of obtaining it.
Coming from a Relicanth user, it does have very good bulk to compensate how late it comes, and has the rare Head Smash/Rock Head combo in later gens. And I love its origin concept.
However, something I can agree that sucks is that no matter if you like or hate Relicanth, you NEED this fish if you want to unlock the Regis. You must waste precious time until it decides to pop up.
F for the Swift Swim Relicanths that killed themselves with Take Down