Not for me. I don't see how it would slow down things.
All of what you write is interesting. I guess it is a matter of taste what each individual enjoys. And whereas I have a clear preference between the two games, it varies. BUT. Even when comparing Xenonauts to the original X-Com in my impression combat comes up short – it does not have the same tension, for some reason, for me. Simply put Xenonauts 1 combat is boring for me. XNT mod for it improved A LOT in combat, it felt tense and engaging, but it still lacked the variety of JA2.
So I guess to each their own, and games are just what they are, and it can not be changed. Devs have their own vision, and they make it come true.
If X2 will be extremely moddable, as is JA2 I guess, it might give ones like me to try and apply our own tastes to the game and share it with others. For now it's still a long wait ahead and we'll see how it will turn out. I just thought I'd share my own two cents.