I understand using a custodian if you absolutely have to.

The issue I see is that there does not seem to be any security level benefit. Sure your phone can be hacked, but so can the website you're custodying with, but worse and more concerning to me, is the influence that is given to any custodian.

I mentioned the banking lobby

I have yet to mention FTX, although they have walked their statements back, the point is that depositors give custodians undue power of influence in a world where politicians are bought and paid for. Maybe maybe if it is combined with a culture like "proof of keys day" then maybe it could be safe enough as to avoid a server side number that does not accurately reflect the backend's cold storage and therefore make a banking lobby 2.0 infeasable.

Sure, your $200 of spending money with a custodian might not be a big deal to you, but thousands of depositors with that same amount, or worse millions, has compounding effects that I don't believe are often considered when people choose to use a custodial solution, a point that is nonetheless moot if you absolutely have to use a custodian.