The only thing I disagree with you is that you say 'maybe'. Of course it's possible to gain on LeanGains, in the end it comes down to calories. As to whether it's optimal or not... that depends entirely on the person. BugAD said it best in another thread...
"As long as you can eat enough calories, you can gain weight/muscle/strength while IFing leangains style (seen it with myself and other I know). There seems to come a point (though you are no where near this) that I've seen with some bigger, more advanced guys I know, where they simply cannot eat enough calories in that 8 hour window to gain weight (over 5000/day)."
Even Michael Keck, a big ass, ripped ass powerlifter dude, wrote up an article for EliteFTS called the Modified Warrior Diet.