Ding ding ding!
I agree, I do not understand why this is bad. When my grandfather went to school, he was a rarity in rural India. My father went to school - he did well, and learned more than his father. I went to school, and learned more than my father. My son did kindergarden last year, and definitely learned more than I did at his age. And this is how things are and should be. Each generation should learn more than what the previous one did. And I don't think my son (or indeed, any of the other kids in his class) found kindergarden particularly onerous. Like all kids, they had their pluses and minuses - some learned to read really early, while others were good at problem solving.
W.r.t summer holidays - I personally think a much better approach would be to have multiple smaller holidays through out the year.