The reason why he admitted it is because everyone knew about it and was talking about it for decades.
There's quite a bit of difference between putting a bit of spit on the ball and what Imran and Pakistan were doing.
And this consistent effort to minimize and normalize it is somewhat revisionist.
No there is not. Both are completely illegal according to the letter of the law at the respective times in question.
Fact is I'm not the one who normalizes ball tampering, it simply was normalized for those in the know of the game. Actually I might be being a bit rough on Imran for calling him stupid for admitting it. Keith Miller openly admitted to lifting the seam. No one gives half a ****. Honestly it's just sour grapes, unless there is evidence leading to a sanction, which as far as I'm aware didn't happen for Imran. And if it was more than sour grapes, there wouldn't be such universal respect for Imran as a cricketer, because he would be branded as a cheat by his contemporaries who likely could still be bitter. But they're not, because outside of those heat of the moment dramas which are pretty normal in cricket, no one really can give a serious **** to a concept of him being a special cheat that stained the game. It's laughable.
There has to be evidence enough that the referees deem it egregious enough to punish in the moment. Otherwise there really are very rarely sanctions for this sort of thing, unless caught red handed in the act. Why, because the culture of the game was one where everyone was clandestinely doing a bit "extra" with the ball, and calling out one group in a "throw the book" letter of the law type way would have opened up the floodgates on all teams.
Pakistan may have been "better" at it, as they had a more targeted goal, and effect that they were clearly going for in a concerted way that others may not have had the right bowling talent to exploit. But everyone was doing stuff to the ball, because there was simply not the eyes to watch and police players 100% of the time, like there is now.
I actually appreciate the culture change that has come with high quality, close up camera footage all angles of the field, because I appreciate a more transparent game where the techniques and skill is more out in the open, and lesser magnitude is placed on skill at this particular sleight of hand. But still it's clear as day to me that in the days before the ball was never being respected in a way that conformed to the full letter, let alone "spirit" of the laws.