I actually don't think recruit is a highroll mechanic. In my understanding, it is the opposite. It will make your draws more consistent after the recruit.
Of course, if you just slam a recruit Card (lets say Guild Recruiter ) in any normal midrange deck, the results are from bad (1 drop) to very good (4 drop). But when you adjust your deck, lets say a druid, and you play the recruiter, then it pulls a 4 drop from your deck (or maybe the Greedy Sprite ). Oaken summons will do that as well, while giving you armor. Recruit Cards are basically reducing the deck size by one per recruited minion helping you getting to your other Cards while teh Plays can still be impactful. Admitted, you can low roll by having drawn all 3 or 4 Drops from your deck when you can play the recruit Cards, but that can be controlled by deckbuilding.
High roll is hoping that barnes pulls Highmane in a regular midrange hunter deck. If you have no 1 and 2 Drops in your deck, you will know that you can only pull 3 and 4 Drops with guild recruiter. If that is still too highrolly for you, then cut the 3 Drops (in Druid that is possible). And afterwards, you will more likely draw your endgame stuff like.
Edit: Btw. I don't think that recruit leads to less bonemares, I think it leads to a more consitent draw of bonemares.
So what I mean with high-roll is that there exists an RNG effect that can have a huge effect on your probability of winning. It can either be getting Highmane off Barnes, or drawing Prince Keleseth on turn 2. Obviously you can also taylor your deck so that the effect of a good or bad roll from your recruit is not huge (then most likely drawing the recruit on the right turn matters a lot). Then it wouldn't be a high-roll mechanic. But the fact that it can be, already makes it.
Example: I can play Barnes in a deck where not a single card has a good effect. Making Barnes practically just 4/5 stats in two minions. The fact that it can be a non high roll card in that deck, doesn't mean it isn't a high roll card.
I am sure some decks will get more consistency out of recruit than what Barnes does. But I am sure others will use its highroll potential to its advantage. Therefore a characteristic of the mechanic for me, is its highroll potential. You just need to imagine recruit in arena to see why.
The other aspect, which I think is very interesting, about the mechanic is the "draw a card" part of recruit. Now I did not value it, because I think it depends on the card, and therefore it is not part of the mechanic. Like you said, the draw a card on Guild Recruiter is great. After turn 5 you want to avoid drawing your 4 or less cost minions, and get your big guys. On the other hand, I don't like it on Gather Your Party. The card will help you to get consistently a solid late game minion on turn 6 (if you stack your deck correctly). But there are few of those, and the draw a card aspect means you have one threat less. Resurrect on the other hand, doesn't reduce the number of game winning threats in your deck. So in that card I will prefer a "summon a copy of a minion in your deck" than recruit, while on Guild Recruiter I'll take recruit every day.
So I personally don't like it. That is not to say it isn't good. Y'Shaarj, Rage Unbound is such a must have in EZ Big EZ decks because in the right deck it can be a very strong mechanic. I'm fine with one or two cards like that, but I believe it should not be as common mechanic as K&C is making it.
I don't like the RNG, High-roll and deck building restriction on it. Now the RNG and High-roll most people understand why it should not be the foundation for tier 1 decks. Deck building restrictions is seen by many as fun, and challenging. Which they are.. for the one guy who does the deck. Then everyone just netdecks that deck, and well... all you just have is a very strong deck. If you have a Tier 1 deck with a building restriction (Prince Rogue), maybe with Eviscerate it will be Tier S, but at the end it is just like any other Tier 1 deck. Very strong, and that's it.
Only aspect I like about recruit is that it forces you to play more minions based on their stats and deathrattle (ie more board orientated) and less about battlecry. I think battlecry is just a spell that forces you to have a minion then on board (nicer than the spell, as it means you care more about the board). In this way it encourages minions like Tar Creeper and less Bonemare. So that is the only aspect I like about recruit.