One thing you left out about the boxer is the insane training regimen, and body conditioning.
Karate-ka usually doesn't train as athletically as Boxers. Nor do most brands of Karate do the conditioning of the body to withstand constant heavy blows to the body.
Your Shotokan tag karate guys dont do this.
So that should be factored in which leads us to ask:
What type of karate?
Goju, or Uechi ryu?
Kyokushin or another standup hardstyle?
Or Karate branch that competes in Kudo where all the sweeps, throws and locking are present.
Which is it... percussive karate, or grappling with strikes karate?
When taken to the endgame 15 to 20 years in...
15,000 to 20,000 thousand hours...
Would Mayweather done well in the UFC against an in his prime George St Pierre, Andy Hug, Joe Lewis Or Wonderboy Thompson?
Or a Prime Morio Higaonna or Kiyohide Shinjo (Mr 9 time All Okinawa Full Contact kumite, Undefeated Champ.)
How about in a no rules, NHB, no referee scenario.
On the street.
After such a long time, the boxing specialist has an opponent who has a vast arsenal, with depth of experience and will begin to find grappling is outside of his boxing skillset.
In much the same way groundfighting forced Standup strikers to evolve.
The 'Te practitioner stands between the Boxer, and the Judoka. Neither Boxer or Thrower Pure but a mixture of both.