Do you ever play unplugged? It's just a thought, but I've sometimes noticed this when people favour a very low action and always play through a distorted amp:- they don't notice what their guitar sounds like acoustically.
If the action is very low, unless you pick very softly indeed, there can be a fair amount of fret buzz. You don't really hear the buzz itself through the amp, but it's choking the strings' vibration slightly and it seems to make the tone a bit thin and tinny.