I haven't seen that CBS poll but if it's true so be it. Denzel will be of course be the more mainstream actor. He's been in way more blockbuster movies. I honestly think it's apple and oranges in thinking who the better actor is. If you prefer Denzel good for you. No one is really going to win this argument. Were just going in circles with it.
I don't think he's afraid of failure to do stage acting. He failed in Nine horribly, but did it stop him from doing movies? I just don't think he's interested in committing himself doing a show 5 or 6 days a week for how many weeks they go for. It's just too much, considering how committed he gets into a role. By the way I think there more risk in failing in movies than failing in stage. You get more attention making a movie rather than acting in stage. More people will see you fail more in the movies. So I disagree with your assessment in that. Even if he went back on stage and failed I don' think it would do damage to his reputation. He'd still be known as one of the greatest film actors of all time. Nothing will change that.
Also DDL has taken risks. My Left Foot, In The Name of the Father, Gangs of New York, There Will Be Blood, Lincoln. Those roles he did in those movies are not guarantee success performances. There's risk to pretty much all the movies he's done. Just because he was great in them doesn't make it less of a risk.