I agree with that, and I put it to use (when I figured out how to ask for it) in my judo/aikido later in life.There are a couple of things that go around in my head on this one. I'd probably learn more in a technical sense if I spent more than 1/3 of the time working with him (rather than him actually trying to beat me). But I think I'd become a better fighter by dealing with that 2/3. The 1/3 of working with should give me something to focus on to get some openings and make something happen. And learning to fight through those times when I can't seem to make anything happen would be powerful learning.
I actually have - at a very early point in my curriculum - a period where new students aren't allowed to fight back. The sparring is light and technical, but they're allowed no offense. I'm getting them some familiarity with just surviving, using defensive tactics when they get overwhelmed, and keeping their head. I think that's important. The OP could learn that (probably already knows some of it - could learn it better) with this guy. And if the guy is working with him 1/3 of the time, that 2/3 should become less intimidating pretty quickly.
Doing randori in the beginning, I didn't really know what I was doing, but I was athletic, strong, quick & flexible from all the other stuff so I figured it couldn't be too bad. Famous last words, right... I should have known better, since I did go through the initiation into Muay Thai.
I was doing randori with my buddy Frank, the school owner, who I'd met at a law school party. Tht's where we worked out that I could teach TKD at his place and trade that off for judo instruction.
Anyway, I'm doing randori with him, and I'm working hard, trying to work him into a position where I could to the ippon seoinage or Osoto gari combo. A combo he'd taught me, it's important to point out. He's talking to me, talking to other people on the mat, gernally not paying much direct attention specifically to me. I manage to get the combo right once and get the shoulder throw. Frank doesn't even stop his conversation with another black belt about some tip or other the other dude was giving his partner.
So, I, in my infinite wisdom, say, "Frank, what is this stuff like when it's done full speed?"
… and he disappeared. Of course, he was still attached d to me, but he'd dropped right between my feet into a double-knee drop seoinage and I went up and over, down flat on my back. It was an impressive Whoomp! I was like... What...? How...? That throw was his pet tournament throw. Didn't hurt, but it did surprise me completely.
Laughing, he helped me up and said, You've got to be careful what you ask for, and from who you ask it. Yeah, no kidding. He Did slow the throw down, show it to me, tell me how it works, etc. Nice guy.
Lesson. You learn a lot in very little time working with (note I didn't say fighting with) people much better than you. I suppose that you also learn a lot faster fihting with people better than you, or you get hurt and just stop.