lesser known reviewers who buy their own products to review are the real deal and speak the truth
That's not true at all, some of those are even more kiss-a

than the bigger ones because they want the sweet deals and don't dare offend a manufacturer.
Then some of the bigger ones can afford to shine a bad light on a product, the manufacturers are the ones who want cheap advertising reaching a big audience, sometimes it even leads to the manufacturer changing something because of a less than great review from one of the bigger ones.
To try and make a general rule, ignoring the personalities of yters and what they actually individually say, is useless. I think most vapers are mature enough to decide if they want to believe a particular review or not.
That someone makes a living with reviewing doesn't by default exclude useful reviews.
Also, a subscription on youtube doesn't mean "I think all their reviews are 100% spot on" it can simply mean "hey I find that guy entertaining", so just the size of a channel doesn't reflect if people actually base their purchase on the reviews.
You'd have to go on a case by case basis, it's not as black and white as big vs small youtubers.