Until 2023 it seemed so, but in almost two years there has been a strong return to the 18650 battery. Many 21700 mods are far too big compared to an 18650 one, and with almost the same size it is often easier to choose a dual 18650. This has also been influenced by the rare pod mods that support the 18650 format, and AIO / Billet-style devices which, in order to remain compact, cannot support 21700
batteries.
I'm sorry to see that in the meantime, mechanical
vaping has practically died out. With the quality 21700 batteries now available, it's really so much more convenient and easy.