According to these articles, Coreopsis definitely benefits from deadheading.
[url=https://findarticles.com/p/articles/mi_m1082/is_n3_v37/ai_13925318/]Flower & Garden magazine[/url]
[url=https://www.thriftyfun.com/tf51453181.tip.html]A Guide to Deadheading Perennials[/url]
[url=https://web.extension.uiuc.edu/gardendesign/maintenance_deadheading.html]University of Illinois Extension Service[/url]