Another factor in those days is there was no salary cap. So if you could build a better team back then, it had a longer shelf life. Theoretically, anyway.
To a degree, this is true, but we have to remember that the NFL draft has been around since 1936. When a guy was drafted, unless the team wanted to trade him or cut him, they owned him during all his playing days. A player could hold out for more money, or to be traded, but that was considered suicide for them in the game. Owners didn't want their ownership challenged, and they pretty much decided that if a team didn't willingly send the guy out, they weren't too interested. Those that crossed that line found themselves being isolated from the rest.
The theory that it was easier to stock fewer teams than 32 now doesn't really work either. When you go back to those old days, there were fewer colleges with top level programs that could produce players, the college seasons were shorter, and the training methods weren't even close to being like they are today. There were fewer teams, that's true, but the talent pool was even smaller by far. Making it more difficult, the scouting of potential players to draft was harder than heck, because they did not have the modern conveniences of today's game.
Since travel was expensive and difficult, to observe players, scouting groups like Blesto came into existence. They did the research, and evaluated players on a nationwide basis. Teams themselves, scouted locally. That's why you'd see guys from schools within the Big 10 as it existed, ending up in huge numbers on NFL teams like the Packers, Bears, and Lions, at least in training camp. The Vikings weren't even a thought at that time.
In 1952, the Packers had 30 picks. In the top ten of them were 5 guys that stuck with the team, and made solid contributions. Beyond that, not to much. It was that strike out rate that pushed teams to pool resources for evaluating of potential talent out there. Ergo... Blesto, etc. There were 33 men on an NFL roster back in those days. Teams were always looking for guys who could play both ways. They were a premium. Quite often, position players, like Lou Groza, who was the Browns offensive left tackle, was also their place kicker. Paul Hornung was the kicker and RB for the Packers, and one of the smoothest of them all was Chuck Bednarek, who played MLB, and center, with the Eagles. He was the last player to play positions on a regular basis, on both sides of the ball. I remember, back in his top playing days, there were those that said he should have been all-pro on both sides of the ball.
If you're a Packer fan, always remember that it was Chuck who stopped Jim Taylor from scoring what would have won the NFL Championship for Lombardi, the first time he guided them to that game. He was an amazing player.
I don't think it's realistic to compare eras to be honest. There are too many things to consider, and if you haven't seen it from all of them, you'd never understand the evolution of how everything has come about. Judge each era on it's own, and you'll be further ahead.
Now, whether or not you want to heed this advice, it's up to you. I'm offering it as someone who has been an avid follower of the game at all levels since the latter part of the 40s, and I've watched the changes, and even been part of it myself, over those years. The level of popularity in football in this day and age is amazing. It wasn't anywhere near as close in percentages of population back in the old days. Take it from someone who's been there.