Let's say ideal data exists in some hypothetical company which will convince you. What would it look like? Asking because this is an area where it will be impossible to get meaningful data unless a big enough company runs an A/B test over a long period of time to measure the impact on career development.

Can't we have data showing career advancement differences between onsite employees and remote employees? I don't understand your attack/sarcasm. We manage to find data to show salary/promotion differences between men and women, or between different races, why not based on the location of the workers?

How many companies exist which have meaningful representation of onsite vs remote employees at various levels of seniority? Can you please name a few?

FWIW, at one of the FAANGs I worked that, HR shared data (promo rate etc) between HQ vs remote offices. But those were still remote offices and not remote employees who could work from anywhere.

Fine, I'll play along and say that you're right: the data doesn't exist - which btw I never contested, I actually asked if there was any data available to back a claim. It is then equally fantasist to claim that being a remote employee at a hybrid company is either detrimental, neutral or beneficial to career advancement.

This sounds like a copout. Lack of data doesn't imply equal plausibility. It means that you need to use other methods of reasoning. And people do this all the time - it's not like every time you're faced with a new situation you go "Oh I don't have any data here, all of my options are equally good". No, what you do instead is use common sense, draw on experience, best judgment, mental heuristics etc. Those aren't as good as evidence based decision making but they surely beat throwing your hands in the air and saying that all of your options are the same.