The mobile data isn't limited in speed, just lower priority as you note.
The fact that Visible/Verizon can even get my (unlocked, full price) iPhone to cooperate in limiting itself in that way in the first place makes me pretty sad.
Eg, if one were to buy a new phone and put a new Visible SIM into that phone and tether their new MacBook with it, and do nothing else, the speed would indeed be limited and this limit would be enforced at the carrier level, and furthermore connecting a second device would be theoretically impossible.
But setting TTL to 65 has been very effective every time I've done it, whereby: The speed of tethering is about the same as the speed of data on the pocket computer itself at any given time.
And I've never actually run into a device limit, even without tricks.
(So yeah, there's reasons for my camping rig to have a USB 3 ethernet adapter for a phone, with USB PD passthrough. I wouldn't care so much if 10Mbps were all that could be accomplished, but things are not necessarily slow like that at all if you're holding it right.
There's a million other ways to skin this cat. A cheap travel router is one way. A cheap USB WiFi adapter on a laptop is another. Setting TTL forever is a one-liner on Windows. And y'all know how to do NAT.)
I get 50GB of data at a higher priority, and then unlimited data at a lower priority. It's not a deliberate or fixed speed limit -- it's just QoS, and after 50GB it's the same QoS as their lower-tier $25 plan always has.
On both sides of the QoS fence, loosely speaking: If the network is congested in an area, things get slow. If the network has good coverage and is not congested, then things are fast enough -- dozens of Mbps in both directions is typical with my old phone's somewhat-limited available 5G NSA or LTE CA modes. (Sometimes, it's triple-digit Mbps, which amusing and frankly overkill for my use.)
With TTL=65, this works fine for me in my neck of the woods. I need tethering when I need it, though I don't need it often. But in some circumstances (some friends and I do a technology-laden form of "camping" sometimes and one of my roles there is to provide Internet) I burn through quite a lot of data.
[1]: Visible is a part of Verizon, and has always been. The chief difference other than different pricing is that it comes with even worse customer support, if you can believe that.