Onboarding for larger accounts – specific KYC/KYB friction points?

Hey everyone, been lurking here for a bit and now have a specific question. I'm looking to move some capital around, substantial enough that it's above the usual retail account thresholds, and I've started engaging with a few different brokers and even a prop firm about setting up. The onboarding process, particularly the KYC/KYB, has been surprisingly varied and, in some cases, quite frustrating. I'm talking beyond just the usual proof of address and ID.

Specifically, what kind of due diligence are others seeing when trying to open accounts with higher balances? Some are asking for source of wealth that's incredibly granular, demanding bank statements going back years, tax returns, and even explanations for specific large transactions. Others seem much more streamlined. Is there a common set of best practices or a 'gold standard' for what they should be asking, or is it really just a wild west out there? I understand the need for compliance, but the inconsistency is making it hard to compare and choose where to put my funds. Any insights, particularly around what's 'normal' for accounts north of, say, mid-six figures, would be greatly appreciated.