Mh, when I played my engineer, I definetly didn't meet a Pyro there - I basically sprinted to the whole left shutter section without ever moving backwards, using high level incinerates by both me and Mordin all the time and sometimes a combat drone. This might have been possible because I maxed out incinerate before my passive (and I also did grunts mission before recruiting garrus so I had more points).
Basically, reasons for this are the blood pack n7 missions you can do before horizon and having 3 missions with quite a lot of krogans or vorcha before in the early game (especially Mordin, but also Archangel and Grunt). Also, after Horizon you can go to Tuchanka and have a great time. There was nothing as easy in my playthrough as doing Mordins and Grunts loyalty missions. I guess I finished them faster than I previously did on normal difficulty.
After I completed this engineer playthrough yesterday, I have to say that Incinerate was propably the skill I used most. Cryo Blast is, of course, great against Krogans and Husks (husks die without further shooting, just like with pull,throw and singularity, after the 2 seconds cryo takes to actually do anything), but it is not that good against enemies behind cover, because they tend to fall down before you can finish them.
By the way: You said that Varren wouldn't be affected by the crowd control effects of Incineration. That is not true, at least not for my version of ME2 - if the Varren is down to health, an Incinerate will make him fall to the ground and he is unable to move. Gives you an easy opportunity to finish him off (For me, this was very important for the N7 mission where you have to save the Quarian - that one's really fun if you pick Mordin and Jacob). Or maybe this doesn't work with level 1 Incinerate for some reason?
I really enjoy watching your vids, by the way. Your adept guide basically taught be how to use my squad properly (and made Samara/Thane my favourite combiantion for husks and collectors), and watching the engineer is fun, because I see what I could have made differently.