As a starter he is more 94-97, he averaged 95.7 last night and 96.1 the start before that and he is starting to hold his velocity and pace through his starts better.
There is also a statistical problem you are running into which is you are using K/9 instead of K%. K/9 will be inflated if a pitcher struggles to get batters out they face more batters per inning which inflates K per 9, whereas K% is inning agnostic and just based on batters faced. Mercado's K% as a starter 2021: 26.8%, 2022: 25.8%, 2024: 25.5%.