You are going to have to better define "win" and "most of the time", because I'm not sure that statistics agree with what you are saying, as I interpret your words anyway.
Per
NFL.com's tracking of quarterback hits, one of the best pass-protecting teams I can find from 2014 is the Denver Broncos; Peyton Manning attempted 597 passes, was sacked 17 times, and was hit on 42 of those attempts. I don't know if NFL counts a sack as a QB hit, but even if we assume they don't (and so we add sacks and QB hits to get the total number of times Manning was touched by a defender), that's a 9% hit rate that defenses playing the Broncos have against Manning. Football Outsiders doesn't offer an exact number of total "pressures" I can easily find, but I can easily find a
"QB playing under pressure" percentage, and they have Peyton Manning as playing under pressure a little over 13% of the time in 2014. Strictly statistically speaking, the vast majority of the time Peyton Manning is playing with a clean enough pocket to make a clean throw and be considered not under pressure.
Let's look at another quarterback who I know plays in a more vertical passing offense than Manning (as I know Manning likes to get rid of the ball quickly): Tony Romo. Romo attempted 435 passes last year, was sacked 30 times, and was hit 53 times (19% touch rate). Romo's under-pressure rate per Football Outsiders is 21%. We know the Cowboys' offensive line is pretty good, and these statistics are reasonable evidence to that opinion.
I'll also go out of my way to find the worst pass blocking offensive line in football from 2014; let's go with Seattle. Russell Wilson is an extreme outlier on the under-pressure statistic at 39% (he's one of five QBs over 30% and the only one above 34%). On 452 drop backs in 2014 he was sacked 42 times and hit 91 times (hit rate a shade over 29%). This is the worst quarterback I can find, and even then, almost two thirds of the time he has a clean enough pocket to not be considered "under pressure", and this even as Wilson's scrambling style of play is inviting more hits than a traditional drop back passer.
It is worth noting, to be fair, that all of these numbers are agnostic of the number of rushers or blockers. Unfortunately, I can't easily find that data; I would assume PFF has it, but I don't have a subscription there any more. PFF does have a
public-facing post from the 2013-14 season looking at the effectiveness of teams' four-man rushes in the general case and found that the highest rate for that season belong to Buffalo, with a Pass Rush Productivity grade of 30.2. I don't know how they generate this score, but they provide the sacks and hits numbers, and the QB touch percentage stat I worked with earlier is at 16% for the 386 four-man rushes Buffalo did. Even Seattle's vaunted 2014 defense, which is regarded as a Top-10 single-season defense of all time, only affected the quarterback 37% of the time (sacks + hits + pressures / drop backs), which while that's a much higher number than any other in this long-winding post I've written still means that they are not getting to the QB on nearly two-thirds of their four-man rushes.
The overarching point I'm striving to make however is that, statistically speaking, pass blocking in the NFL is actually pretty decent and pass pressure isn't prevalent to an extreme amount. This data shows that defenses shouldn't be winning but so often, regardless the number of rushers, assuming that a quarterback is properly managing his pass protections, protecting from overload blitzes by sliding his protection, keeping an additional blocker in if the defense is sending more rushers than there are OL, etc. The data doesn't support that defenses should win "most of the time".
If you can find data for number of four-man rushes vs five blockers, I invite you to post that, as I'd be very interested to see it. I'm plenty willing to be wrong on this, despite the novel I've written here.