I have the T470 (with swappable battery) and the T14 (newest T-line Thinkpad without external battery).
Weight difference is minimal, size difference is minimal. Yes, there is a difference, but I don't notice it really. And I'm someone who actually lugs the laptop around, on buses and trains and while riding a bike. Most people don't even really carry their laptops, maybe from car to office and that's it.
As a person who actually carries their laptop around, I appreciate the swappable battery. Train rides are much less anxious, no need to find a seat with a plug nearby, because I know I have an extra battery.
The T14 is definitely less portable. There's less ports as well, which is quite annoying. The only downside of the T470 is the screen - I like to work outside and a higher brightness screen is crucial. If I could have the T470 with a better screen and AMD CPU, I wouldn't bother buying a new Thinkpad.
I don't know why they call ultraportables ultraportables. Are they marketed for people who sometimes lift their laptop off the table and who are bothered by the "extra weight"?