The friend who replies slow but always shows up is worth more than ten who reply fast and flake.

Replying fast is cheap and turning up is expensive, and people quietly confuse the two. A quick response feels like closeness because it arrives when you want it, but it costs eight seconds. Being there on a Saturday when it would have been easier not to costs an afternoon, and that is the one that tells you something.

Rate people by attendance rather than speed. Then check which of the two you have been lately, honestly, over the last month. The slow replier who always comes is a better friend than the fast one who never does.