Nor do most humans adapt a lopsided or haphazard approach to measuring seasonal tides.
According to Wikipedia:
"The day (May Day) was a traditional summer holiday in many pre-Christian European pagan cultures. While February 1 was the first day of Spring, May 1 was the first day of summer; hence, the summer solstice on June 25 (now June 21) was Midsummer."
You apparently didn't read the article.
Now, I will be the first to admit that there are varied interpretations (just as I view Imbolc or Candlemas as the last Winter holiday in the old tradition because it falls within the Winter season, others likewise may view it as the first Spring holiday since it recognises the first stirrings of Spring within the Earth and the lengthening of days). And you are also correct in the idea that our forebears long ago, when most could not read or write and possibly did not have access to a calendar or almanac, recognised the seasonal manifestations at different times. No argument there. (Harvest Home, for example, is correctly observed in our 21st century on the Autumnal Equinox, but say a few centuries ago, especially in more remote communities, it was likely celebrated once the majority of the harvest was in... within the Autumn season, but not necessarily on a specific date.) However, those who did have access to the information and the astronomical science behind the seasonal cycles used it, just as I would think our less knowledgeable ancestors would have.
My point, again, is that while the weather in our region may not match the astronomical season, and while we may generalise the seasons with phrases such as, "Spring came late this year", scientifically the seasons manifest themselves like clockwork, astronomically, regardless of local weather patterns. Perhaps it would help to view the astronomical designations as turning points, or harbingers, of the seasonal changes, which would be reasonably accurate. After all, even though Winter begins in November, many areas are still enjoying Fall, some even with Summer-like temperatures.
I'm not saying I don't get your points, I just can't agree that the astronomical calculations which denote the seasonal changes are not scientific.