Aside from that, it’s definitely not the only or best strategy. Buying gold early can usually edge it out, and it’s very vulnerable to curses.
Another factor is that with experience, your opponent will either recognize what you’re doing and defend by buying the cards you’re wanting, or get their own engine going to beat you if they learn from their mistakes.
Most games are won by buying out the provinces, yes, but the three stacks win is there for a reason and is great for catching opponents off guard when the kingdom’s right.
IMO it's an terrific 1-on-1 game where meaningful strategic and tactical decisions are made, but I find the game a lot more "fun" with three or four players (five players takes way too long)
Most players start off playing big money too much, move into playing engines too much, and then move back toward simpler strategies more often.
Some boards don’t even really have a good engine available, usually for lack of +actions.
The baseline strategy however: Only buy province, gold, or silver. You might be surprised how strong it is. It is also boring if you play with friends though.
You can't cycle through your deck multiple times in a single turn (barring the existence of sifting cards which given this was your first game I assume not) so you were probably playing a rule wrong.
Whilst it is perfectly possible to build efficient full deck draw engines I will bet big money as a beginner that you took wayyyyyyy too long to build an execute your engine.
Not sure what you mean by cycled through your deck multiple times, but if you meant all in 1 turn, then you definitely didn't play correctly.
Any action cards that are played are put in the play area, and aren't moved into the discard pile until the Cleanup phase. Also, the Buy phase only starts after the Action phase has ended. ABC (Action, Buy, Cleanup).
Once you've drawn your entire deck and need to draw more, then the discard pile is shuffled to form a new deck. Once that's drawn too you'll be left with an empty deck, no discard pile, and the rest of the cards left in either your hand or playing area.