I actually think that's a very plausible possibility when considering how little access one actually has to the region they're in while playing - even when given every obstacle-clearing TM in the book, there are still some unsurmountable obstacles that keep you on certain designated routes and areas - but are these obstacles that are unsurmountable to your character, who is in the canon lore a child, truly impossible to get past by everyone in the region? Seems unlikely to me.
And consider the Move Tutor. There are several moves which you can't get on your pokémon without outside help from that person. So it seems quite plausible that there are techniques of move teaching which aren't directly available to the character you play as, and perhaps not all of them are ones people are willing to share with you. Maybe somewhere out there there's a move tutor who can teach dragonite barrier, but they live in one of those locked buildings, and won't open their doors for nosy kids, only sharing their techniques with the stock of trainer who has clout, such as an Elite. Or maybe these Elite trainers made it to their position by figuring out training methods which a novice like yourself hasn't, and used their discoveries to their advantage.
So I think calling NPC trainers who do things you can't "cheaters" isn't exactly fair - it runs off the fallacy that the limitations of what a 10-year-old kid can do should apply to everyone, which definitely doesn't apply to real life, so probably doesn't make sense to apply in the game's universe either. Sure they could be said to hold an unfair advantage over you by being able to do things you can't, but then again, it could be said the inverse is true - in several games, your character has the extraordinary luck to have fate grant them with the chance of capturing an elusive and highly powerful legendary pokémon. Sure your peers you face in competitive battles all have had that same chance, considering all of you are iterations of the same highly fortunate 'chosen one' of a main character, but your NPC peers? Not so much. With a few exceptions, you are the only person anyone around you in-game ever seen who managed to get their hot little hands on an uber pokémon, so to them, you very well could be the "cheater" who has an unfair advantage.
tl;dr: calling trainers like Lance "cheaters" is conflating the storyline metagame with the post-storyline PVP metagame, which I don't think necessarily makes sense.