last estimates I read mentioned 400k covid research papers, diabetes had over 1.5m and 'cancers' , as varied as that topic is , has many many millions of papers.

The intensity of research was high, and the technology yielded quick high quality results, but there isn't much reason to consider it to be 'the most thoroughly studied disease' -- maybe if you go by some arbitrary figure like 'megabytes of genomic data sequenced' ?