At 1/2 a build per weekend, a single level takes more than a year at a single chapter. Even hitting up every game at 4 or 5 chapters isn't likely to get more than 2 - 3 levels a year.
I would like to point out a couple of things:
I few years ago (2011 or 2012, I think?), I mapped out all announced events across Alliance and found that out of 52 possible weekends, there were 45 or 46 weekends with an event going. Someone with the means could Pay-No-Play (or Season pass) every single one of those. I know of an Owner who gobbied/pay-no-played/attended every possible event and went from being circa level 35 to level 48 in the span of that year (many owners have 'agreements' to allow each other play for free in each other's chapters; that year, they took this to mean "free gobbied events" - those Owners aren't Owners any more AFAIK).
I myself have 3 season passes going right now IIRC, plus I gobby OR and play in SEA, and I know there are a few more chapters/season passes I could get, but don't. (Season passes are really cheap for what you get!) I'm a LOT higher level than I otherwise would be if I was only getting build/XP from the chapters I could actually play in (OR and SEA) without getting on a plane.
I know of at least 3 people right now who blanket/play more than that. I really don't feel it's as big a long-shot as you think because those very old characters that are currently 50-55 didn't have Pay-no-play and Season Passes for the first 15+ years they played.
I know characters that were started less than 5 years ago who are level 30 or higher now. Back when the game first started, even after 5 years, nobody was even remotely close to that.
I'm not saying that every player does this, or will do this, but it is possible and more and more players are taking advantage of "pay for build" options. I've been on one particular Season Pass since it was first offered. The email that I get every time they have an event has a list of everyone who has the pass on it. The list has grown every year and the last one I saw had like 15 players on it. That's a lot.