Definitely not seeing Alphabet's 20:1 split in July 2022 when I glance at Yahoo Finance charts - you sure about that? Or are you saying they're adjusted for some corporate actions but not for others?
EDIT: OK, I see there's a note that close is split-adjusted but not dividend-adjusted.
Dividend adjustment wouldn't really matter in this study. The price discount at dividend ex date should match the price increase post earnings announcements, so it's netted and disappears once you compute >=quarterly returns.
The price increase at earnings announcements is (to a first order approximation) indicative of the extent to which the company's earnings exceeded the market's expectations. It's as likely to be positive as negative. Otherwise you could buy the company's stock the day before the earnings announcement and get yourself some free money.
I use TradingView for most of my charting and at the bottom right side there's a button labeled "adj". Clicking it will toggle whether the chart you're viewing is dividend adjusted or not. Very convenient for quick off the cuff comparisons of returns.
Using SPY I can easily see the non adjusted returns from the bottom of the GFC to the top in 2021/2022 were a little over 600% but then accounting for dividends see it's actually a bit over 800%.
EDIT: OK, I see there's a note that close is split-adjusted but not dividend-adjusted.