SmartThings starting to feel like Homeseer?

Nope.

SPECIFIC differences between "SmartThings Classic" (the V2 app) and “SmartThings (Samsung Connect)” (the V3 app)

(As you may recall, my very first use case for home automation was unlocking the door.)

If there new App usage was really discouraged, then Samsung could and would have disabled login to new App for existing accounts who already use Classic and all confusion would be averted.

They can’t do that because only the new app works with Samsung smart televisions. The classic app used to, but that broke back in the fall of 2018, and the fix is to use the new app.

But we should take discussions about the new versus old app to the following thread:

The point of this thread is that smartthings has gotten, if anything, more complicated over the last four years. It’s still very powerful and very flexible, so there are people who will definitely want to use it – – and web core is an awesome addition – – but it’s certainly not any closer to plug and play than it used to be.