Modulation: Real-time modulation (like using the mod wheel for vibrato or tremolo) feels more organic on the hardware than on a static sample set. Finding the Best Results
Filter Sweeps: A SoundFont often uses a generic digital filter, whereas the JV-1080 hardware filter has a very specific, stepped character that is hard to sample perfectly.
For many producers, the "better" in the "Roland JV-1080 SoundFont better" argument comes down to workflow and accessibility. SoundFonts are lightweight, load instantly in almost any DAW, and don't require the bulky rack space or aging power supplies of the original unit.
To make your Roland JV-1080 SoundFont sound truly superior, you shouldn't use it "dry." The secret to the 1080's success was its internal effects processor (EFX).
Zero Latency: Unlike hardware which may require external MIDI syncing, SoundFonts trigger instantly within your digital environment.