It's simple. You don't own any Bitcoin after buying a Bitcoin ETF. You own ETFs and they are similar to such a land which somebody else own but you plough it and assume that it's yours. It's more like putting your money into someone else's bag and let them decide what they buy for you.

Simply useless.

It only makes sense in a registered account. AFAIK, can't self-custody in registered account in Canada. ETFs are less risky than MSTR and miners.