Absolutely can and is main incoming for a lot of poker players. The luck factor is pretty much nullified when you put 6+ hours a day grinding. Your weekly/monthly sample size becomes so big that its pretty much impossible to face a losing month, (if you are winning player obviously)
I agree here. However, it does take a little fast math and a whole lot of discipline. Bankroll management is key to maintaining a working game because proper bankroll management decreases the effect of variance. Always get your stack in good with positive expected value, never play against the odds, never put more than ten percent of your roll in play at once, and grind, grind, grind! Volume is the secret ingredient: more open tables and longer sessions equal larger profits...the law of large numbers hasn't been proven wrong yet.