Getting rid of (mostly) all your coppers looks fine, there's not really anything more expensive then $4 you want anyway.
By the time you even consider a 2nd purchase of a ruined market the game has already been decided.
However, there are quite some early turns where you return 2 coppers rather then 1 estate. I wouldn't do that in an apothecary-ambassador deck.
5/2 is obviously bad but I'd open Ambassador/- rather then Potion/-.
I think if your opponent...
a) opens Amb/Amb or
b) opens Amb/Potion but buys 2nd Amb on turn 3 and Throne Room on t4
... you're in really bad shape.
Around turn 18 you sort of "have the game sealed". I'd now get Saboteur rather then Monuments.
I think you want to play with more throne rooms and probably 1 or 2 smithies at some point.
Advisors are also fine, probably better if you don't have enough throne rooms.
This is not the kind of game I'd call a slog, but I guess that word lacks a good definition.