Not sure where indeed is getting their numbers, but I can assure you levels.fyi are well calibrated. Glassdoor also has weirdly low estimated salaries.
I haven't done that specific analysis but stock based compensation is given out in public quarterly financial statements. See here for example that Google spent ~9.35 Billion (!) in stock compensation last year: https://www.macrotrends.net/stocks/charts/GOOG/alphabet/stoc...
What does the estimated salary bill for each of these companies come out as and how does that stack up vs. their public declarations?