re "one containing a bulk of the stash".
I feel like it just depends. In my own case, that's never been true, over a decade and multiple different wallets (even just talking about the cold storage wallets). First I don't tend to move a nontrivial amount in one step, I break it up. Second, usage over time (and if you use bitcoin at all, you're going to use your cold storage wallet sometimes), breaks it up further.
So I don't have any data on it, I can imagine it's true for *some* people, I'd bet it's not the majority, but 🤷♂️ who knows I guess.
Even if it were the majority, say 60%, that had *most* (not all) of their BTC in one address, we'd still be nowhere near "number of addresses with >1BTC = number of users with >1BTC".