For families with substantial assets, retirement planning is primarily a tax-structuring problem.
At higher asset levels, the difference between an adequate plan and a strong one is rarely the return assumption. It is the tax treatment of the withdrawals.
That means building the account mix years in advance, using low-income windows for conversions, and coordinating charitable giving with the years of highest income.
It also means keeping the estate plan in the same conversation, since the accounts being optimised are often the ones being inherited.