Your comments about 83b elections aren't correct.

You file an 83b election when you early exercise your stock. Pretty much all startups will allow you to early exercise, which is when you exercise options before they have vested. The 83b filing doesn't need to be within 30 days of the grant, but does need to be within 30 days of when you early exercise the options.

What the 83b election says is "I early exercised shares, and here is the fair market value (FMV) of those shares." Assuming that the FMV is the same as your strike price, then you don't owe any taxes then or until you sell the shares.

In my opinion, any early startup employee who can afford to do so should early exercise at least some of their shares. You do risk some cash, but you potentially save a lot of tax under the current tax code.

Also, as other people mentioned in comments, if you owed $200K in taxes, then those shares are significantly in the money. I'm guessing they are ISOs and not NSOs, which means that you owe the $200K under the AMT calculation.

Under the AMT rates of 26%, you are looking at shares worth at least $800K, which means that you stand to make a significant amount of money. Which makes sense given that you were willing to put up the $300K.

Also, you likely did a lot better by buying the shares when you left. If you had a 10-year exercise window and waited until the company had a liquidity event, you would be taxed on a significantly higher basis when it came time to exercise the shares, and you would pay tax as if the shares were regular income rather than paying at the AMT rate and using the AMT calculation.