The Elements probably all tie into each other in some way. You can be loyal and honest, share laughter and kindness, etc. To say generosity and kindness are similar isn’t a stretch. I do agree with what most people have said so far in that kindness is typically a nonphysical gift like time or compassion, while generosity typically is a physical gift such as money or food.
Who is to say kindness and generosity have to be limited to this, though? You can be kind by giving a friend a physical gift and you can be generous by giving someone your time. This thread makes me wish this sort of thing was elaborated more in the show to teach kids that qualities are not limited to one type of action. It would have also been interesting to see an episode where the Mane 6 are criticized for going “off their Elements”.