so, imho there are two kinds of randori: rep randori, and shiai randori.
for rep randori, you're workshopping or repping your tokuiwaza. you trade off being uke with your partner. you focus on free movement as uke while tori focuses on setups and timing. when the throw comes you just take the fall. the BJJ corollary would be flow rolling.
for shiai randori, you're going at it competition-style.
now, shiai randori is your best look, but it's shitty practice - usually, the more dominant person will consistently have the upper hand, while uke will spend most of the time defending. as an uke, yeah, you get better stuffing throws, but unless you're outclassing uke to begin with you're not gonna make much progress.
a good analogy is how we practice armorball here in murica - you can't do live, padded practice all the time. you've gotta spend time running routes (uchikomi), and you want to be able to scrimmage without killing each other, otherwise you're gonna end up with a bunch of stuffed plays and injured players.
whenever i randori with a less-skilled person i tend to be very playful and considerate. i could just fucking maul most people, but they wouldn't learn anything. i wouldn't just GIVE them a throw on a half-assed attempt, but i'm also not just completely shutting their shit down.
when i get to randori with a good black belt, that's when the gloves come off. even then, some people are looking to rep stuff. in that case, you wanna give good resistance but you don't want to waste the whole round playing defense.
so as far as progression, when i want to workshop a throw i'll try to use timing and positioning rather than outright strength and speed. i'll rep it with a few rounds of lesser ranks, then go balls-out against someone shiai style. even then, i'm not just looking for *any* throw i can find, but specifically working my grips and entries for the throw i'm trying to improve. it really helps your game in that regard - much better to whole-ass one unfamiliar throw than half-ass your tokuiwaza for gym wins.
does that make sense? i babble...