Having the cost be 2 means that everyone gets access to it in the first two hands with out there being much swingy-ness in terms of the initial shuffle.
Maybe an argument could be made for 3 or 4 in the sense that everyone would still have access to it, but 5 just seems too high.
But making it 5 takes it out of the opening hand most of the time. That’s why most of the best cards are 5.
I’m not 100% sure it shouldn’t be 3 or 4 but it definitely shouldn’t be 2. And I’m fairly sure that if it trashed 3 cards instead of 4 it would still be extremely playable (given how many times good players take worse trashing than that in the first round) and that the play testers back then just didn’t know the game well enough yet to understand.
It already has that. If you draw 2 coppers in your first hand (and thus five in the second or vice versa), you can start out with the awesome five-cost card and chapel.
I would consider the Dominion League[1] to be serious competitive play, but it doesn't require that (also the current online client doesn't support that, presumably due to lack of demand) but what it does is to balance which player starts first, which can often lead to wins since in the end the game is often decided by a single turn.