I feel your pain. I’ve been using SmartThings for a long time now and IMO the whole home automation market is still immature.
I find the Hue lights work great with ST, and I also have a Yale front door which works very well with ST. Sensors etc work fine but eat batteries too quickly for my liking (which is not a ST issue of course).
Regarding the thermostat, unless you have a specific need for control via home automation, I would just buy a normal wireless thermostat and set it up with a weekly program. If you do need that integration I would look at what’s available from the likes of Nest etc, but I think the ZWave/Zigbee market might be a little empty which takes ST out of the picture.
I don’t think ST brings anything special - that ship has sailed. What I will say in its favour is that if you are technically competent you have access to the code, can chop and change device handlers etc.
I’m too invested in ST to change and as I said, my lights and my front door work great 
I’m very happy to be proved wrong by the way!