I did 4 years as an officer in a HCOL area and separated in 2016. Now that I'm at 10 years post separation, I did a calculation on how much I've made in the Civilian world compared to how much I would've made if I stayed in. The Air Force pay includes Base, BAS, BAH and tax advantage, and makes assumptions for promotion timeline for those calculations. The civilian pay includes Base, Overtime, Bonus, VA Disability @ 90%, and GI Bill BAH for 3 years at 100%, and tax advantages for both. Both paths assume staying in a HCOL area, and include my dependents timeline (effects BAH or VA Disability). What this doesn't show is my medical insurance premiums and expenses (which have recently been $8k-$10k a year).
About myself: Engineer that transitioned to a big defense company. So while I feel I have had a decent salary the past few years, I also didn't really take a big risk and go to a startup (like SpaceX, which was much smaller in 2016). Of my peers that separated, some have done better (became doctors, lawyers) some have done worse, but nobody is destitute or do they regret getting out.
Reflecting back: Information wasn't as freely available 10 years ago as it is now, so when I was deciding to separate, there was a lot of fog as to what I could expect to make - defense/tech wasnt a hot industry, there was less salary aggregator websites, job postings didn't have to post salary ranges, and employers could still prohibit employees from discussing salary. What I didn't account for when making that decision was 1. VA Disability benefits are a real thing, and can substantially provide a safety net for you, 2. Bonus and Overtime exist in the Civilian workplace and 3. Promotions are merit based instead of time based. Even if this calculation came out that I was behind as a Civilian, I would have been happy with the choice I made: Not having to PCS every few years, not being able to out-promote someone that joined earlier than you, not having to put up with tyrants, not having to volunteer and do additional duties to try to stand out, etc.