The motor should still start without an AFM, but it'd run like garbage, with lots of smoke, highly unstable idle, etc. And if you have spark, the ECU should be fine. Happy to be corrected on that one though.
Spark, fuel and compression is all we need. Sounds like you've covered all three bases already. As Adam said, plugs will foul with fuel, and it is probably flooded, but WOT whilst cranking should sort that - and the boggy performance you mentioned means it is something else.
A dodgy coil or a fouled plug or two will start start, but just run like crap. Sounds like spark is covered.
When a fuel pump dies, the motor will start for *just* a second or two and then kark it. One or two blocked injectors will start start, but again run like crap.
Sammy what you've described seems like a vac leak, just like you thought. Is there any chance you could have missed something?
Mark