I think what plenty people get wrong with "my performance is better with those mods" is that while maybe for their current state the mods add, lets say +100 rating, they hinder long term improvement. And that is the point here. They hinder the development of game sense, they hinder the adaption in your brain that is necessary to read an entire map from icons alone, etc. When you learn to ride a bike, eventually the training wheels have to come off - there is no way around it. As another example you could perfectly learn Sentons only, air slot only, seraphim only, perfect 15 min build order, strat rush only, and jump easily to probably around 1700 rating (or even more). That would have the same problem: You dont develop the skills and adaptive abilities necessary to perform in ladder/tourney settings (where different maps are enforced, faction bans, people will know your replays, etc).
Maybe I should write a guide on how to improve in games in general.