Did he have every single front end technology listed on his CV?
Front: Angular, Android, Ionic
Middle/Back: Springboot
Lang: java, c/c++, c#, python, typescript
Anyway.. my point was this.. 4yrs with 12 month job hop. I've done job hop 1.5-2yrs initially but part of it was due to contract or situational. A typical junior takes 3-6months before they start delivering on own.. fast forward to a more mature setting with tech stack changing.. if you hoping ever 12 months.. that means u need to be delivering value by end of month 1 or 2 (I usually aim for 1 month). Now when does he learn the new stack and show value ? And then if he is leaving at month 12 that means he might not have seen consequences of bad dev because he is gone when the stuff hit the fan
i dunno maybe i'm just old or like the long haul where you prove yourself over time instead of impressing in interview but hopeless. Might be why most of jobs are via ref or network and rarely via interview (unless old school dev types).
PS. Post getting experience with good software eng.. slapping on newer frameworks and pushing salary upward happens fast from what i've seen,