To me it's absolutely the telephoto. It's what I miss the most on my iPhone Air (coming from 15PM, and Pro phones for years). Previously, when looking back at my photos, I was about 90% Main lens, 9.9% Telephoto, 0.1% Ultrawide.
Lack of a Telephoto lens is what I tell people is probably the make-or-break of whether the iPhone Air works for you. Given the non-Pro iPhones have had just Main and Ultra-wide for years, I think if Apple had given the Air the Main and Telephoto, it would've done much better as positioning and pricing as an "almost-Pro" phone.