Improve with dailies only?

Speed/Rapid chess tends to be primarily an exercise in moving pieces around faster than your opponent while avoiding checkmate, in hopes that his/her clock runs out sooner than yours. There is little time to think about what you should be doing.
It makes sense that taking more time to think about what you should be doing would promote improvement in your chess skills.
One way to significantly improve your chess is therefore to play mostly longer time controls, including "daily" chess, so you have time to think about what you should be doing.
This is not to suggest that you should necessarily play exclusively slow time controls or daily games, but they should be a significant percentage of your games, at least as much, if not more so than speed games which do almost nothing to promote an understanding of how to play the game well.
Here's what IM Jeremy Silman (well-known chess book author) has to say on the topic...
https://www.chess.com/article/view/longer-time-controls-are-more-instructive
By Dan Heisman, famous chess teacher…
https://web.archive.org/web/20140627052239/http:/www.chesscafe.com/text/heisman16.pdf
https://www.chess.com/blog/RussBell/dan-heisman-resources
and the experience of a FIDE Master...
https://www.chess.com/forum/view/general/how-blitz-and-bullet-rotted-my-brain-don-t-let-it-rot-yours