This !!!
I made the same mistake as junior, thinking that staying at same place for years will get me to somewhere, spend 4 years as junior thinking "ok, it will not be that year, next year i will be mid for sure", nope, changed jobs and found pretty quick that not only my title was unnecessary delayed, i was in fact so grossly underpaid that my next role payed me almost 400% more
I've never switched. Philly is a terrible area for tech jobs. Same company for 10 years. Just barely touching $100k now.
What would you say is the "perfect interval" to jump companies ?
I doubt there is one.
The general wisdom is switching every two to two and a half years in order to maximize lifetime earnings.
As soon as a better offer lands. You gain nothing by waiting. After some jumps the interval at which better offers come your way, will naturally increase: there are very few jobs that pay well, respect the workers and so on.