it is more or less what I have been doing, but it only works on missions where you have to destroy something. Actually, I find avoiding enemies pretty fun sometimes. I think it is very hard to engage everyone.
Well performance will not fix itself, wait for a patch :D
I noticed that variety of missions is less in Xcom 2 than in XCom EW. You have Assault Facility that has no timer and the rest that has direct timers or soft timers (like Terror Missions).
Missions with timers come in 8 or 12 turns and all play the same. Only smaller exception is where you get to escort the VIP from round 1.
Even defend this device has you start far away from it and plays the same as Destroy Object in 8 turns and get away mission but timer is not turns but life of that device.
I prefered a lot more the defense missions in EW vs EXALT where you defend two positions and fight vs enemies coming from all sides.
Also since many council missions were not timer based, having timer based missions like bomb defusal made them interesting. Here it all feels the same. Even enemy reinforcement mechanic is worse than in Xcom EU and EW. The Thin men dropping from sky unannounced and all over was much more interesting and harder to deal with (especially in first play when you didn't know where they would drop).
I am not complaining about difficulty of timed mission, just that they all feel same after you done 20+ of them.
As the game is now, even with randomly generated levels I feel less drive to play it again after I finish it once than I did with Xcom EU.
I was afraid of this when they started coming out with details of the game and my fears came true.
Actually, it is not completely true :
The timed missions where you have to destroy something are pretty low risk, because you can usually scout without triggering anyone, and destroy the objective with your snipers (or grenade the wall with your phantom ranger, and destroy the objective with the sniper), and then camp happily.
The missions where you have to protect a location usually don't force you to rush too much, although it depends on how accessible the objective is.
On the other hand, the missions where you evac with a VIP are really hard. You don't always have enough time to deal with every enemies (especially if you did trigger some dark events adding more enemies), and cannot use snipers much.
But I agree that the missions felt more different in XCOM:EW.