As a pro funk player I can get good sound on any bass that has low action and fairly new, fairly bright strings. In the early days I cycled through multiple basses (passive and active), multiple eq settings, compressors, etc. Turns out the answer was in my hands the whole time. Most pro bassists and guitarists play with their volume louder but with lighter touch which sets you up to play with good dynamics. If there’s one aspect of the ‘settings’ that would be it. But, like most other skills in life, you have to just keep doing it year after year.
My current setup (but by no means the ‘secret’): Passive jazz bass (tone knob rolled back 20% for slap - not always), Flea strings (GHS Boomers), multiple different amps, any ol’ compressor to add a bit of compression, prefer mids scooped, bass and treble cranked. That’s my ideal setup, but, I can slap really well on a Precision as well so it’s not the bass. And, I like slapping in an active or passive setup - passive is just easier in live settings (for me).
I don’t own one, but, if there is one bass which is ultra easy to slap on (for me) it would be a Geddy Lee Jazz Bass (Fender or Squire). Whenever I play one at Guitar Center I find it really easy to slap on. I play a Fender Jazz Pro II