I intentionally booked a longer layover in London and it totally changed the trip

This is the sweet spot of layover planning: using the hub as part of the trip rather than treating it like dead time you just have to endure.

The best intentional layovers usually happen in airports where massive route choice gives you room to breathe instead of forcing constant clock-watching.

I started doing this more once I accepted that an extra few hours can improve the whole trip if the airport and city are a good fit.

The key is respecting terminal changes eating the entire layover enough to keep the plan disciplined instead of trying to squeeze in one more thing.