They are mistaken on both counts. Even if you're in an uncrowded niche it'll be several months, even a year or two, before you start to earn money consistently. And this tends to happen indirectly, as a result of the heightened profile and authority your blog gives you.
Really, there are only a couple of reliable ways of making money directly from a blog. Probably the main one is still serving Adsense ads or its alternatives. Yes, you can make some cash from occasional affiliate sales. But even those will be few and far between unless you develop quality, ongoing relationships with your readers, who then buy products you recommend.
Then there are sponsored posts -- which are kind of like advertorials paid for by companies. That's not something I'd recommend because Google doesn't like it. And if you do too many then you start to undercut your authority.
So in the end the best way to monetize a blog is indirectly. That is, use it to lift your profile and build your authority in your niche. Then offer your own products and/or services.
This sounds pretty straightforward. But that's only if you know this before you start blogging. While there must be people in this boat, I'd say they are in the minority. The harsh fact that a blog works best as a springboard to income (as opposed to a method in itself) is certainly better known than in the past. But it still not the prevailing view for some reason.
So, if you didn't have a strategy to begin with, you've basically got to keep blogging, and cobble together one as you go. Everyone is different, of course. But here are a few suggestions that might be of use:
Offer tutoring services in your niche. This is a good option because you can charge by the hour. And while distance is no barrier these days because of great tools like Skype, you'll tend to find more success if you offer the service locally. This is because people like the personal touch. They'll refer you to friends too. (I know this works well because I teach people social media privately in my city. I have a locally oriented site for this, and the attached blog has helped a lot in lead generation.)
If you have a Wordpress blog that you've built yourself, you could do installations for other individuals and businesses. Of course you don't have to have a blog about Wordpress to do this but that would be ideal, of course.
Since social media promotion is a crucial part of blogging these days, you could also offer services in this field for business owners too time poor to do their own. (That's something I might even try offering off this site, BTW. But at the moment I'm too busy, and having too much fun, doing my own!)
Blogging is writing, of course. So why not use your blog as a means of gaining freelance writing assignments? Offering these services on your blog is a better approach than bidding for gigs on freelancing sites in my opinion. While you could almost certainly get work quicker using the latter method, you could wind up with an enormous amount of work to do to a very tight deadline, and be paid poorly for it. If you use your blog to fish for gigs, however, you can do things more on your own terms.
So there are a few approaches to think about. Any other blog monetization methods you'd like to suggest?