Avoiding heat and reducing time spent fully charged address different stresses, so I wouldn’t treat them as alternatives.
Batteries also have a limited cycle life, but a cycle isn’t counted every time you connect the charger. Using 50% of the battery, recharging, and later using another 50% adds up to roughly one full cycle. Frequent small top-ups don’t automatically wear it out faster.
Optimized overnight charging delays the final part of charging until closer to when you need the phone. An 80% limit reduces time spent at a high charge level.
If 80% comfortably lasts your day, the limit makes sense. If you need the full capacity, optimized charging is a practical compromise.