I worked a swimming pool decades ago, and saw parents giving their pre-teen kids some drugs like Guronsan (https://www.drugs.com/international/guronsan.html) before swimming competition. It might be legal, but it was sending the wrong signal to those kids. That a pill could give them a boost or an edge.
"But at that level, everyone is operating under the same rules"
No they are not. In reality it means, the athlete with the better chemist behind him, meaning the one with the not yet traceble substance, will win.
But at that level, everyone is operating under the same rules. That's just the nature of competition, no? People will take any edge they can while following the letter of the law, if not the spirit.
Hell, even in the context of "on their own, unassisted", some countries directly support their Olympic athletes in terms of training, coaching and facilities, while other athletes have to pay out of pocket for that sort of thing and figure it out on their own and thus are more "unassisted", but there are no rules about that...
At the end of the day, all you can hope for is that the rules are applied justly & transparently.