You didn't even realize these two claims cancel each other out.
How can you claim the lack of defensive 3 seconds would be helpful unless you're giving up jump shots?
And if zone defense makes shyt easier on the offense, then they would simply stop doing it. Most players score on jump shots in today's game because they HAVE to, because zone defenses neutralize iso and post play and cut off driving lanes too easily unless you have a bunch of jump shooters to open up the court.
No, because you weren't allowed to be in the paint unless your man was in the paint and you weren't allowed to double off-ball. You could only double the paint if you stayed on you man until the other guy got the ball and then committed completely to the double. It added a delay time that made shyt way easier and it made it more risky to double because you left you guy wide open (and the other defenders couldn't hedge towards them), which is why guys like McHale and Barkley could take their time developing a slow-ass play on the block against a helpless defender.
Even when they did throw the double as quick as possible, it was usually ineffective. Here's an elite high IQ team who would win the title (the 1984 Celtics) trying to defend against truck driver Jeff Ruland. Despite the fact that he's slow as fukk with no elevation and no range outside 8 feet, they pretty much feel helpless against Ruland one-on-one and throw the double-team immediately every time a pass comes in. His teammates don't help by giving him zero spacing. And yet he scores over and over again because the weak-ass doubles are out of position almost every time.
Here's another example of out hard it could be to double back then. 6'6" Michael Jordan is backing down 5'3" Muggsy Bogues. They clear out that side and Muggsy is totally helpless. They don't want to double because they have to go too far. So they have to leave Muggsy on an island against a player 15" taller than himself, though surprisingly he makes an elite play and strips MJ.....only for illegal defense to be called because the defenders were hedging into the key too long.