Welcome. You are doing great, but you are right that you need a better tax strategy.
A 401k is not irrelevant to your strategy. Firstly, it is tax-free savings - that is never irrelevant to someone on a high income. Secondly, it is not as though as 401k isn't yours: it is, and the way you use it is to become financially independent before you otherwise would.
Imagine maxing out your 401k, plus employer match, for 10 years. Put those amounts into a calculator at a safe average stock market return (ie 4%, for present purposes, or a bit less if you are risk averse) for the number of years until you can access it without penalty. That gives you a lump sum at that age which will give you an income, calculated at your safe age, until end of life.
Now, all the tax-paid stash that you are accumulating has to do is to get you to that retirement age (plus any retirement top up that isn't catered for by your 10 years of 401k). That tax-paid stash can be a lot smaller, because it doesn't have to accommodate your old age needs. So you are FIRED sooner, and less likely to be rich when you are retired.
Why don't more people buy discounted shares and sell immediately? 1) They don't have access to discount purchases, 2) They don't have spare cash to buy discounted shares with, 3) They don't have access to the relevant the financial information, or don't understand it, 4) They are too risk-averse.