Hello! So I'm gonna start by explaining what it is I'm doing exactly, and then move onto a few theories I've come up with on how Quick Ventures actually function.
So recently I decided to go scorched earth on getting the Peregrine Helm, and also the Onion Doublet set and Explorer's Tabard set, but mostly the Peregrine Helm. I have seen a few posts on reddit and here that people have gotten it from Quick Ventures, however there were no screenshots just word of post. What I have gotten confirmation is that the Onion Doublet is still in the loot table. So I believe it is likely that the Peregrine Helm is there as well.
So with that goal in mind I am creating 40 characters, with 10 retainers each, with the purpose of sending as many retainers as possible and the results are starting to get interesting.
Now it has been official stated by SE that ilvl and equipment doesn't matter for quick ventures (I think it was during a live letter). However, it seems that retainer level itself might play a part in what the retainer brings back. Specifically the green and blue equipment the retainer brings back appears to a level range near what the retainers level is.
This is why the player can't fund your retainer ventures solely off what the retainer brings back until later levels. You simple can't get enough seals off the Low Level gear. This also means that in order to get the Explorer's Tabard set the player need to limit themselves to around lvl 50 on whatever class your retainers are until you get the set.
Now the second theory has to do with the rarer lvl 1 white gear (cosmetic gear). I'm still early into this "challenge", and I could be entirely wrong, but it appears that the likelihood of a player getting this gear is also based off retainer level and seems to increase as your retainer levels up. I have one character with lvl 90 retainers and that character definitely gets more cosmetic gear than my other characters.