This is almost an impossible question to answer, because the ratio is going to (drastically) change based on personal circumstances.

For example, we are getting ready to buy a house, so we are overly cash heavy right now because we want to put a significant down payment on the house.

Someone who is going to retire might decide it best for them to have a heavier than normal cash position to use as a cushion.

People in certain industries and/or house owners vs renters might have different cash emergency funds based on their personal beliefs in what they will need to use it for.

All that said, I believe in a solid four legged stool for retirement.

1 - pre-tax traditional 401k

2 - after-tax roth 401k

3 - after-tax brokerage accounts

4 - cash

All of these have their pros and cons. And, those pros and cons will be different for groups of people based on their situation in retirement (not to even mention early retirement). I feel you need resources in all four buckets so that you can take advantage of those pros and cons planning for and the executing retirement.

I am no expert, but I feel a lot of people just think of the now. Taxes now. Money now. Growth now. And, that is all very important. But, you also have to plan (as best as you can) for the future and what those things will/might look like during retirement.

YMMV