From my experience
Plusses in striking. I can't really speak on boxing as my boxing is limited in training.
This pertains to Karate/TKD. Over 15 years and still going
- gauging of distance
- learning of head movement.
- leg kicks, mid-section kicks , high kicks and mixing of punches.
- you can end something with one blow
-knees and shins. Elbows.
- disabling someone's legs is a quick fix
- if you're flexible enough the kick combos are a beauty and blinding.
- limbs build up resistance to getting hit
- blocks become an attack
- sweeps, joint locks.
- weapons training
Grappling (limited experience. 2 years and still going)
- very taxing on cardio
- you can spar more at a bit higher intensity due to less likelihood of injury vs striking.
- you spar hard at striking and you may get a broken bone(s) or put to sleep.
- how to avoid takedowns and get off your back (pause) or having limbs taken away.
- the grappling transitions are a beauty and can work someone over.
I can honestly say that neither one is exponentially better than the other. I'm biased to striking as all fights start standing up.
Contrary to popular opinion, you can with the right understanding of the danger you're dealing with avoid takedowns with good stand-up and quickly put a grappler in no man's land if they have zero striking experience.
If you have zero grappling experience getting manhandled despite martial arts experience is very humbling.
The most important thing is to get some training under your belt. Anyone guaranteeing a specific timeframe for a black belt/Dan is full of shyt.
It can range from 3 years to the most dedicated of folks (4-5 days a week) to 10 years.