Why do people say this? I've had members say the same thing to me. What I get from this is back in the day when car audio was at it's peak we didn't have good systems until now.
To me, just because things are new and up to date, doesn't mean it's better. It's like an incandescent light bulb, the main concept hasn't changed, maybe minor changes but not necessarily a better product. My point being, there haven't been any major breakthroughs since speakers and equipment were created and refined...the wheel hasn't been reinvented. Everything made today is still based off the same basic principles
As to the OP, I feel you and what you have said. The one thing that comes to mind is you stated the only difference that has changed is the weather...that is the biggest and most important aspect of differences. The atmosphere changes make the biggest impact on everything, especially in audio and the way a car performs. This would be my thinking on why you see the differences that you do. it could change day to day, hour to hour. Maybe I missed something that you stated but I would think these factors would be the biggest culprit.
However you may be onto something with what you discovered about the mics and changes with heat/ environment as well, IDK
I feel many older things were better than what's available today. However, to get equal quality today takes a lot of money it seems. Times have changed too quickly and the economy is too messed up IMO. Today, people want everything cheap...so manufactures have to have something that fits the bill and we know what that gets us. Too many variables at play