Well your question was how many pro-bowlers do we need on the OL? Ask any QB in the league and they would prefer to have every single spot of that offensive line as stout as possible. Now with regards to what happened last year - yea Tyron gets hurt, you adjust but you also have to contend with the loss of a talent like Zeke. Now your entire offense, that was built on being a ball hogging, time of possession dominating offense is required to change into something else entirely. Can't really do that, especially not with a second year QB. Realistically Dak should be still carrying a clipboard and learning behind Romo, instead he is having to start and learn as he goes. Only so many adjustments you can make.
Last season Alfred Morris averaged 4.8 yards a carry (Elliott 4.1 yards a carry). Not saying Morris is better than Elliott but 4.8 yards a carry is hugely respectable and pretty much any QB in the league would be more than happy to work with that.
There are ways around keeping the ball on offense than just having to rely upon one running back.
The way I see it is that the O-Line in 2016 was just exceptional and I mean truly amazing. Prescott hardly got touched and the running game was so strong complemented by how strong the O-Line was resulting in a lot of 2nd and 3 or 3rd and 4 type scenarios as opposed to 2nd and 8 and 3rd and 4 type situations which he couldn't execute last season.
I agree ideally he would still be holding a clipboard but they went all in on him and essentially forced Romo to retire so we are left with a situation which I think will be similar to last season on offense. Stop start in a lot of games with the defense playing above their level, keeping us in games until they get gassed by having to do too much due to the offense not firing.
I think people underestimate just how amazing the O-Line was in 2016 and I include O'Leary in that as he was great in creating holes for the running game but the point is, I think Brian Hoyer would have pretty much done what Prescott did in his first season and last season was a more reflective view of his ability and production I expect going forwards.
That isn't a cheap shot etc just my personal observation and I hope that I am wrong as if i'm not then we have wasted a Superbowl window in my opinion.