That has been true for us up until the pandemic - at least in our case. The combination of the school taking extra precautions and parents not sending sick kids to school is working. We've had our daughter in daycare for months with 1 total illness (minor cold). And in that case I believe it was from taking her to outdoor dining. Kids seem to touch every part of those restaurant high chairs which are never sanitized.
I get your point, but it's really a stretch. There's been no reported cases of covid at our school and the symptoms matched common cold. Sure I guess there's a chance it could have been some mild case of covid the same as it could have been flu or some other illness.
Prior to the pandemic she used to be in a tiny school with 4-6 kids and 2 teachers and she was sick seemingly every other week. The difference seems to be the combination of teachers sanitizing everything, keeping kids in smaller groups, temperature checks, and parents not sending sick kids to school.