So, then, who are the right people for the kind of financial questions that require experience but don't need an ongoing relationship? (For example, someone who has an existing IRA but would like to convert it as to later take advantage of backdoor Roth conversions - it's a complex modeling exercise that's probably simple for an expert but hard to get right for someone who will need to do it precisely once in their life.
That is the problem. Everyone wants single-time advice but it isn't possible to actually distribute that product profitably in the current structure of the market.
Regulatory costs are very high, this means insurance costs are high, etc. Marketing costs are extremely high in financial services too. If you are going mass market, you are paying hundreds of dollars for leads...how do you make that work if you can't charge much and need to acquire your whole customer base every week?
This is why most of the market is underserved, why rich people end up owning all the high-yield assets, and why the only real solution is having very large institutional pools of capital for most retail savings (i.e. like Australia's superannuation funds, which produced a level of wealth for the average consumer vastly in excess of the US with lower levels of GDP per capita, relatively poor penetration of financial markets, etc.).
For me personally, half the benefit of handling your finances correctly is that with the knowledge of one thing often comes learning about something else that might tweak your financial strategy or at the very least increase your options in life. For something like a backdoor roth strategy or when it might make sense to utilize isn't something I personally would want handled for me. I would want to understand the decisions I make and potentially learn something important along the way.
Financial literacy doesn't seem optional for the wealthy from my perspective. There's too much to gain by having it and too much to lose by neglecting it.