I'll actually defend $5 cost > trashing 3 Copper, but only if you're hoping you get lucky. In the absolute best case you get a dream draw and buying the $5 cost early makes up for not trashing 3 Copper. (For example, on turn 5 you draw Hunting Party, discard your entire deck, and Chapel your hand.) The problem is that outside of the lucky cases I think you're worse off than just trashing the 3 Coppers.
When you trash 3 Coppers, sometimes you get bad shuffles and are forced to buy a bunch of Silvers, then lose because you keep drawing your Chapel with your Silvers. But I think most of the time you're not that behind - you hit the 2nd Silver, draw 2 Silvers + Copper at some point to buy the $5, and then you're only a bit behind.
Awaclus, you really need to learn to argue better. Nobody cares when you say the same thing with slightly different wording, even if you think it's true.
If I draw Steward + 4 Copper, I'm almost always trashing 2 Copper instead of buying a $5 cost or Gold. And this feels like a more extreme version of the same scenario.