Annual sponsor fee of 0.25% for management fee in IBIT (iShares Bitcoin Trust ETF), the NAV is going down every year, this won't happen if someone buy spot BTC but to be fair it's far better than keeping it on CEX because ETF have SIPC if you buy through brokerage. If CEX fail, that's the end of it.
If we are talking about something like Coinbase, then if it fails - everything fails, that's the scenario where you won't be safe no matter what or where you hold it.
Besides, iShares hold BTC mainly in Coinbase Custody as well. But Coinbase is the definition of ''too big to fail''.
Not just ishares either, 9 out of the 12 Bitcoin ETFs in the US picked Coinbase custody to hold their BTC. If anything happened to Coinbase, it'd be a real disaster for the market.
https://cryptobriefing.com/coinbase-dominates-spot-etf-custody/It's not hard to see why they go with ETFs, either. Institutions and companies have strict requirements to meet when it comes to risk management, financial reporting and asset custody..ETFs let them get exposure to Bitcoin without overhauling their existing processes, and they stay compliant with SEC regulations at the same time.