There's good reasons the traditional brokerages have so many rules...
The facts seem to be RH saw a opportunity to prey on uninformed individuals by making investing seem "cool" and "stupid easy".
RH deliberately did not do a good job of A) Putting limits on newbies (like no margin!) so they do not get themselves into trouble and B) Explaining the more complicated concepts behind what RH was allowing literally any mirror-fogging human being to do.
People are always going to be uninformed about some things, yes we should minimize that but we shouldn't make services available only to the rich because of it.
Definitely not a good comparison.
But someone who has initiated a money transfer and then used that pending money to buy stock, technically on margin, is not getting themselves into margin-related trouble. There is no good reason for there to be limits here.
Margin accounts have a different legal definition and regulations.
Robin Hood is actually pretty unique in that its cash accounts are always restricted to settled funds; instead they decided to optimize for margin accounts that don't allow for increased leverage. Which is not something other brokers optimize for that I've seen.
If an account allows those, it is a margin account.