oh! I wish I had read this before I also take a look at twig and had the same results, I jut checked it against an experimental blog code, using a framework contributed to the slow times as well.
As much as I personally like the default SMF template system (not because is easy to use but because is pretty much the only template engine I ever used) I also can see the benefit (for themers) of using an "inverse" method, aka, wordpress template where PHP is inside HTML. But thats somehow ugly and I def wouldn't want thousands of <?php ?> tags just filling up space.
As for template engines like smarty or twig, I have mixed feelings, when I see a twig template, my mind immediately goes "oh, yet another pseudo code and syntax I need to learn", perhaps it is just me being reticent, I still need to find a cute HTML template and port it over to twig code to see if I'll ever be interested on it.
And I agree, the templates def needs to lose some weight if they want to fit in a pretty and fashion twig engine that not only applies for normal templates but for mobile versions as well, there is just too much displayed data that makes it terrible difficult to implement a really nice, clean and objective mobile version.
Sin talento no busques grandeza, porque nunca la vas a obtener.