The argument amounts to …
There is almost no upside to owning multiple IRAs. There’s just complexity without benefit. Whatever entity is managing your various IRAs, one is best. Close the rest and move your money to the good one.
The logic for 401ks for retired people is the same; more than one is just complexity without benefit. And in fact closing your one 401k into your one IRA is even simpler, net of the loss of the creditor protection so ably explained by @Tamerlane just above.
For someone still working (that’s you) they can’t avoid having a current 401k with their current employer. And they’re stuck with whatever provider that employer picked; good or bad. If it’s a good provider, there’s no upside, only complexity, to maintaining old 401ks elsewhere. Better to roll them into this one. If this one sucks, then better to roll all your others into the best one of the bunch. Again, “diversification” of brokerages / 401k management companies is not useful in any way.
In fact, for someone in your expected shoes (planning to still be working while old enough to be generally subject to RMDs) who did have 401ks from prior employers, those would be subject to RMDs. Unless you rolled that money into the plan where you’re still working. In which case it’s shielded from RMDs until you stop working for that employer. Somebody could job-hop to age infinity repeatedly rolling their 401k into their new employer and avoiding RMDs forever. Until the Grim Reaper catches up to them.
And once fully retired for good, other than the liability / bankruptcy shield, there’s no reason to maintains one IRA and one 401k. Simpler to roll the 401k into the IRA and have just one IRA and zero 401ks. Simplicity is good as we slide into dotage. Complexity is bad. It’s not any deeper than that.
I do not understand this question / point. I fear we’re failing to communicate. My fault.
Once you’re old enough to need to do IRA RMDs, you compute your IRA RMD based on the IRS age table times your total IRA balance of all your IRA(s) combined. Then withdraw that total from any combo of one, some, or all of your IRAs. e.g. if you have two IRAs, one with $5K and one with $10K, total that up to get $15K. Then multiply that $15K total by your RMD age factor, call it 4% for the first year, to get $600 for your IRA RMD. Then pull $600 all out of one IRA account or all out of the other or pull e.g. $100 out of one and $500 out of the other. You can choose any combo you want for any reason sensible or silly. The IRS only cares about the total IRA withdrawal(s), not how they’re distributed amongst your IRA(s).
401Ks are different, in that the RMDs are per-account, not per the total. So assuming the same scenario … Assume you have two 401ks, one with $5K and one with $10K. The 401k RMD factor based on your age is exactly the same as the IRA factor: 4%. But …
First you multiple 4% times the $5K balance in your first 401k giving $200. And you must withdraw $200 from that account and no other. Then you multiply the same 4% factor times the $10K balance in the other 401k, giving $400. You must withdraw $400 from that second 401k and no other.
For the same $15K total in IRA or 401K the aggregate RMDs will be the same each year: $600 in our example. What differs is solely how that $600 may be, or must be, distributed between your multiple IRAs or 401ks.
Make sense? Have I been responsive or did I misunderstand your point?
Reminder: 100% of this discussion is ignoring ROTH accounts which have no RMDs.