The TL;DW is that bike gears are often not low enough.
If you give me a lever long enough, and all that.
The assumption here, though, is that climbing is all you care about, and not an average speed across a ride.
I'm by no means fast but I certainly won't make it to the pub for lunch if my gearing was as low as it would need to be for me to make it up a hill using the same amount of effort if expend to travel moderately on the flat...
Fair enough - I suppose it's a caution borne out of experience of the awful roads by me - I've had a lot of unsealable punctures on the roads near me (from gashes to a bit of glass that wiggled around just enough to not seal).
As a result I always caveat advice to go tubeless - for "proper" punctures (anything more serious than a pin prick or snakebite) tubeless can be a can of worms, and give people a sense of confidence that inner tube users don't have (wisely).
Granted it's also down to tyre choice (you can pry my patched panaracers from my cold dead hands) but a tyre pissing sealant and air is much more of a hassle to deal with than an inner tube in my experience.