Classes are one example. They're a big one, in D&D.
The theoretically unrestricted possibilities of a TTRPG are a very real appeal. But they don not cause the system, itself, to become infinite, imponderable, or immune from reasonable evaluation.
As I mentioned, above, improving balance by removing an option is possible, when that option is invalidating multiple other options, but replacing the offending option with a balanced one will necessarily be a greater improvement in balance.
Balance isn't about restricting options, it's about maximizing real options.
Verisimilitude is arguably about restricting options - someone wants to play a certain concept, you object that it will ruin your verisimilitude.
Verisimilitude can be placed in conflict with anything at any time, since it is subjective and arbitrary, by the very definition you game, of 'making since' in spite of fantastic elements.
In other words, you judge what you think makes sense, and then arbitrarily excuse some of those things as fantastic, while demanding other be removed.
Well, 4e was a reasonably balanced game, and over 2 years, presented 23 classes, 2 of which were arguably sub-par, but still usable.
5e is a decidedly imbalanced game, and, over 10 years, has presented 13 classes, 6 of which are on an entirely different plane of sheer power and versatility from the others.
And then, there was 3.5 ....