There’s certainly a learning curve involved and it’s definitely less convenient until you deal with enough issues that you’re comfortably past that point. I don’t know anyone who has turned back once they got up to speed though. The ones most likely to balk and go back to tubes IME are the riders who have been changing tubed flats for dozens of years and can do it without thinking, have dealt with every possible permutation of a tubed mishap, etc. but for whom tubeless is a totally new set of considerations. I think if you took a brand new rider out and trained them on roadside tubeless repair from day 1, they would probably find it easier than learning roadside tube replacement from day 1.
The OG worm-style plugs can require a bit of technique during insertion to make sure they can handle road pressures (which should pretty much be sub-80psi on all road tubeless setups anyway). First time I encountered that was the only time I would have needed to resort to a tube (thankfully OH was 10 mins away and already in the car at that point so I phoned for rescue).
Stan’s Dart was a step up and seemed like a really innovative solution, but I had some issues with those too and it often required a few stops to add air before they held. And I never trusted them enough to go back out on a subsequent ride without removing the plug and patching the tire instead. I suspect their proprietary chemical reaction thing only works with their own brand sealant and that there’s some kind of chemical treatment on the plugs themselves which loses potency after carrying them around in a saddle bag for months.
Once I stopped avoiding Dynaplug due to cost and finally ponied up I’ve never had an issue since. The barbs on those plugs hold so much better than anything else that they’re really not even in the same league as the competition, especially at road pressures. At least for the kind of tricky punctures that might prompt some to fit a tube.
I’ve now installed and removed enough tight tubeless tires that I’m not concerned about being able to get them on and off at the roadside, but I think of it very much as a last resort in a ‘ride over, get to a train station / meeting point / etc.’ kind of situation. I must be at something like 20,000mi and 5 years of road and gravel riding without needing a tube now, which I feel is enough to make even a fairly long call-a-friend pickup acceptably rare. Before fitting a tube I think I’d even try to nurse a barely-holding plug at less than half my normal riding pressure to get to a bike shop or train station or something, but I haven’t even had to do that.
A couple years ago I switched my spare tubes to Tubolitos to save space, but I’ve still never fitted one. (Pro Tip: unless your spare tubes get used often you should store them in an old sock or something so they don’t get holes abraded into them while rattling around in a saddle bag. And as someone else said above, there’s no point carrying a tube unless you also carry a tire boot - if you don’t need a boot then you don’t need a tube). For a recent gravel ultra I carried a standard Tubolito, an ultralight Tubolito, and the Tubolito patch kit. All items are still in their protective socks.
I do know a few road riders who mostly just do club runs and drop rides which keep them within a couple dozen miles of home and so don’t carry anything other than a CO2 and a Dynaplug, and I don’t even really see them having to call for help often enough to cause domestic unrest. I do hope they carry a few more spares than that for a big day out though!