(I am aware of the difference between soundfonts and samples, soundfonts are just organised, like a sampled instrument preset in a sampler)
All composers tend to have their own rules.
Some may use presets on synths and freely available samples, because maybe they want to sound like everyone else, or want real instrument sounds but don't have the instruments.
Some composers may want to do their own completely original thing so have their own original soundbank.
For people involved in Music Production/Composition as a profession originality is very important as record companys tend to chose a certain producer due to his sound, created by his palette of sounds. If a lot of people in the music industry may be using Kontakt/Sampltank samples having someone which their own soundbank can be good.
But for people who use samples I think you should tweak the samples/kits, even if a tiny bit like EQ, FX, maybe some dynamic FX on individual drums/samples.
"All existence you see before you must be wiped out : Dream, Reality, Memories, and Yourself"