Overall, Google has a tendency to under-level on hire. If they need a leader for a small engineering team and they're not sure the candidate has L6 experience, they'll hire at L5 and let them get promoted if they exceed expectations. Far better to do that than to hire at L6 and then have them fail to meet expectations.
But, I agree that there are fewer checks and balances when it comes to leveling. The hiring committee is going to recommend a conservative level based on interview feedback and resume - they don't know the context of other peers in that particular org. It's up to the manager to push back or fight for the candidate if they're hired and outperforming (they can be re-slotted quickly if needed).
Point being: there are more checks and balances to ensure that women aren't being rejected more often than men, given similar background and interview performance - but it's not clear there are checks and balances to prevent women from being systematically under-leveled.
Another issue: the levels in this lawsuit are pretty high - L8 is equivalent to director, L9 is equivalent to senior director. We're talking about the top 0.1% of the company in terms of seniority.
The committees here would all be L9 and above, so basically all senior leadership in the company, which is less diverse than the company as a whole. Also, not nearly as many people are hired at this level, so the committees won't have nearly as many numbers to crunch.
My personal feeling here, having worked at Google, is that Google does far more than the average company to try to make hiring and compensation fair. That doesn't mean there aren't mistakes sometimes - but it's because individuals are still biased, and company-level efforts to minimize bias overall don't eliminate it at the individual level.
I have a very easy time believing that this particular individual was underpaid. That doesn't mean most women at Google are underpaid.