I think it's a false dichotomy that great architecture and fast iteration are at odds. In fact, great architecture is what allows fast iteration to happen.

Yes, simplify your system by using as few moving parts as possible. But that also means don't use bloated frameworks that silently slow down your iteration pace with technical debt.

So many startups I've consulted with were stuck with having to redo core architecture right when they found market fit. It's a tough position to be in. The main rule to follow is that good design allows better design to happen later, it's worth investing in that