Good point! I guess the prudent FAANG engineer would buy a total market fund and then short a portion of their employer to net out the overexposure. Would sure feel odd though!
A safer approach would be to just purchase a fund which excludes tech. Personally I'm too lazy to do this and just have a total market fund :)
On the other hand, if you are 100% certain in your investment thesis that you don't want overexposure to any company including your employer, you could try direct indexing the rest of your portfolio e.g. buy S&P 500 except for your employer. Selling on vest is another simple alternative you could consider.