I think the issue with grappling is mainly to avoid the ground. I mean, everyone generally accepts that in a multi-person street-fight, one of the last places you want to be is on the ground, either GnP'ing or getting punched/kicked etc etc... you're far too vulnerable to everyone.
Everyone's seen the footage of the Turkish boxer holding off 4 people in the street, but he was able to do that because there was a lot of space. What happens if he couldn't? A crowded bar, a narrow alley etc etc. People are going to get within clinch range, and as early UFC's showed, if two people with no trained takedown ability grapple, the one going for the takedown normally gets it. If a world class boxer doesn't have room to move, then while he may be able to one-punch some people, what happens if someone grabs him from behind? He trips over someone? Etc etc.
And that's the other point about why grappling is necessary. If you do get taken down, you want to be able to get back up again as quickly as possible. If you don't know how to do that, then you probably won't be able to.
Perfect "bodyguard" for a street-fight? Chuck. Yes, his standup is terrible in terms of technique, but he packs one hell of a punch when he does land... and he'll be standing up throwing punches all night. Apparently he used to roll with the anti-fa back in the day (which is why is genius that Stormfront supported him against Tito), so he's been in the odd ruck before as well.