It's wiser to buy hardware no sooner than 6 months after release. Do you agree?

Used to be an earlier adopter. The thrill has worn off over the years as I realized that early adopters are only marginally better off than beta-testers and have made greater financial outlays. These days I'm content with buying only after products have been confirmed to be deliver on their promises. It has become a habit to read the reviews, especially the 2 and 3 star ones. The 5 star and 1 star reviews tend to be too biased to be given too much credence.

Depends on what you optimize for. If you want a good price/performance ration then waiting even longer might be a good idea.

Hardware revisions for retail are a special topic though. Depending on the particular device or part, a later hardware revision might just mean that the manufacturer found cheaper parts for assembly. Most consumer devices are tested quite thoroughly because competition is high. So it is not easy to say, but usually waiting a bit leaves you with advantages.

I agree on a general basis, with the caveat that sometimes there's a sea change that warrants being an early adopter (the Apple M1 laptop series comes to mind)

With major OS and software upgrades though, I am all for waiting at least a few weeks till the first patch release comes out.

No. Bought 16" M1 Pro Macbook Pro on day one. No regrets. Best computer ever bought.

Never regretted waiting.

Whenever Apple introduces a new design or some radical new features, then I believe it's generally a good idea. I don't think it matters much if Apple iterates over an existing design.