[ This is coming from someone who haven't played a mainline Pokemon game since Ultra SuMo. So most of my words are coming from past experiences and gameplay videos I saw of later gens. ]
I second with Wisehowl in that Pokemon has a very deep game mechanics that steadily increases in each generation, but never really put their step into their own mechanics. While each generation tries to make the process of raising your Pokemon for competitive environment (such as IVs, EVs, Egg Moves, Natures, and Abilities, held Items), they don't really challenge the player to ever touch any of the mechanics except for type advantages. Like having trainers, even most of the boss trainers don't have teams that synergies with their types like using items, weather/field effects, hazards, or set ups. There are few exceptions, but that's just exceptions than the norm.
The only time in the mainline games were you actually use the games mechanics is not in postgame, but in a small section of battle tower. and even then, that fells more rigged than challenging.
Besides Pokemon romhacks like Radical Red and Elite Redux and other Monster Tamer games that's largely inspired by Pokemon like Disc Creatures, Cassette Beast, Coromon, Dokimon, Omega Monsters and so-on with different approaches on the mechanics of pokemon.
While there isn't a problem with Exp Share as long as it help average the level of your team (such as how BW/B2W2 adjust exp depending on your mon's level and the opponent), without worry if they might accidentally overlevel their whole team and just steamrolled the whole game. But that is on the whim on what the player want to do since it was an option to activate (unless it's built in in the game in SwSh & SV, again I haven't played them).
