There are no hard rules. In general a microservices architecture tends to enforce segmentation which makes it faster to iterate on features that only impact a single service. But coordinating larger changes across multiple services owned by separate teams can certainly be slower.

Monolith architectures often degenerate into the proverbial "big ball of mud" over time. But if the team has the discipline to maintain proper design through continuous refactoring then they can retain the ability to deliver features with short cycle times.