If you’re interested, here are some stats from the approval studies for semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound), so you can see how fast participants lost weight over the course of the studies.
In the semaglutide study, participants weighed ~105kg/230lbs at the start and lost about 500g/1lb per week for the first 20 weeks, then it started to level out slowly. (You can skip to figure 1.)
In the tirzepatide study, participants started around 94kg/207lbs and lost about 400g/0.9lbs per week for 24 weeks until the weight loss slowed down. (Reference figure 2).
(These studies aren’t directly comparable to each other since they had different study populations, but this should give you a ballpark idea of how fast people on these meds lose weight on average.)
You are mostly right that the weight comes back on, but at least in the time frame studied (up to a year after stopping) a not-insignificant amount of weight stayed off.
For semaglutide, participants lost ~10kg/22lbs over 20 weeks during the run-in period, then when switched to the placebo gained back ~5kg/11lbs over the next 48 weeks. Participants who stayed on semaglutide lost even more weight, leveling out around 20kg/44lbs total over 68 weeks.
And a similar story for tirzepatide.. Lose 20kg over 36 weeks, then gain 10kg back over the next 52 weeks for a net loss of 10kg/22lbs vs total weight loss in continuation group of 25kg/55lbs over 88 total weeks.
I will say that the final ~5% bodyweight loss in the semaglutide study or almost 10% bodyweight loss in tirzepatide study is still a big deal for a lot of people, and a lot of diseases and disease risk can be mitigated to some extent by weight loss of 5-10%.