use hundreds of wallets, which makes it nearly impossible to determine how
many funds are actually at the exchange. If you try to determine the amount
by looking at the order book, you should be aware of the fact that many shady
exchanges use spoofing to give the impression of support "walls".
I also have no idea why you think that it is possible to see what the big holders
are up to. How would you track their movements? I don´t think that this
is doable and cryptocurrency trading markets are just as opaque as
stock market trading.
I have to say, I'm speaking about ETH tokens,
"Most exchanges use hundreds of wallets", that's not true most of the centralized exchanges use few addresses (public) and have many internal addresses for tokens for example binance, they have https://etherscan.io/address/0x3f5ce5fbfe3e9af3971dd833d26ba9b5c936f0be#tokentxns, and few other token addresses. Thanks to transaction costs exchange can't have many public addresses, because then they would have calculate fees with transaction costs. Most of the transactions at centralized exchanges are done by internal transactions between internal addresses which are of course like you said untraceable. But that doesn't mean you don't know what is deposited to the exchange (withdrawals are thanks to the different withdrawal addresses difficult to tract but not impossible).
"If you try to determine the amount
by looking at the order book, you should be aware of the fact that many shady
exchanges use spoofing to give the impression of support "walls"."
Agreed, that can't be done.
"How would you track their movements?"
Same principle like exchanges, depends how many big holders there are I would argue in current state and network-speed, its possible to send, trader notification that "big holder" moved his money, even before the transaction is confirmed (for like top 50-100 holder addresses). You know then, who is sending tokens where and how much they're worth, obviously he can just send his tokens to exchange and back (or to the other address), just for fun, but how many big holders really do that.