- It does not have 3D Touch
- It does not have a Barometer
- Front facing camera is still 1.2mp
- Does not offer the 128GB model
- First iteration slower TouchID sensor
- No dual domain pixels
- No LTE advanced
- considerably cheaper than the phone that has those things in addition to having a much more manageable size for those who want the smaller phone.
I see that all you've done there is listed the exact hardware specs that make it different to the current 6S in order to find something wrong with it to say "It's not worth buying" or "I's unworthy of a keynote introduction" (as I saw someone legitimately type without irony on these forums a couple of days ago).
I mean, maybe I'm wrong, but it's hardly like people were make-or-break on the inclusion of the barometer.
Given that the phone is £174 cheaper (64GB 6S vs 64GB SE) I think those compromises are just fine, especially since the majority of those looking to buy one are coming from the 5S and prior models.
Also what's all the fuss about the original Touch ID sensor? Assuming it's the one I have on the 5S right now, I can't say I've ever had a problem with it being "too slow". If it were any faster then clicking the home button to glance at the lock screen would be impossible unless I faked it out with a non-approved finger (and thus risked disabling TouchID with repeated failed unlock attempts).