So given that, to see significant ROI you need to find genuine experts in how to use each form of media.
So, even if it is technically possible to do well in a given media, if it is really hard to identify who is a genuine expert in that media due to it being new and full of snake-oil merchants, then you are likely to do better in a more established field.
You're correct that there certainly a lot of snake-oil merchants out there. But they're not just limited "new" media channels. Just as many slimeballs in the traditional world.
I'm going to get crucified for this, but paid advertising is somewhat analogous to software engineering/developers. There are many languages/platforms/technologies out there. Some old, some cutting edge. Each one most likely has it's own syntax/terminology, patterns, approaches etc.
So when hiring a full stack engineer, you look for someone who cuts pretty deep across a few key areas, but can also roll up their sleeves across the stack if need be. Example: Ruby Expert, Getting into Angular, and knows how to provision AWS if need be.
Same thing with full stack marketer. If you know Google Adwords, Content Marketing and a bit of PR are your core, then optimize your hire for that.
There is already a bunch of startups around this problem. A friend of mine works at Adaptly which, among many others, let buyers who don't know social media advertising essentially outsource the expertise required to do so effectively. It's always seemed a bit like snake oil to me, but maybe its a real problem.
There are literally hundreds of "startups" doing that for social media advertising. Hundreds for search. Hundreds for display, and not just regular display, but RTB(sarcasm)! There are tons of startups doing it for native ads. And don't forget video, seo & content marketing among others.
Add on to that, the partner/provider lists of "startups" that sit on top of one or many of those tools.
And let's not forget about the 1000s of agencies out there to roll it all up.
There are tons of snake oil salesman, and many good tools and people in that list. But as with pretty much any ecosystem, it's 80% crap, 10% meh, 10% bam.
And there is no one right answer. Just like no absolute answer to Python vs Ruby.
So whenever I see articles like, "facebook ads bad! look what they're doing!"
Change it to, "facebook ads bad! Look at all the things I'm doing wrong, but don't even know enough to know I'm doing wrong!"
>it is really hard to identify who is a genuine expert in that media //
Arguably it's easy - if their advertising works then they're good. If you notice a marketing company then they're doing things right to some extent (at least WRT your demographic).
So, even if it is technically possible to do well in a given media, if it is really hard to identify who is a genuine expert in that media due to it being new and full of snake-oil merchants, then you are likely to do better in a more established field.