That's not true, if your traffic is targeted around a specific niche, then you want display ads to also be targeted around the same niche to increase your CTR.
Example: You wouldn't run ads about mortgage info on a cat website. Instead, run ads about cat food, or maybe other cat products. This way, your traffic is more likely to engage with the ads, giving you a higher CTR which will in return pay you more money. It's simple really...
Also, a CTR of 1% is terrible and you should really optimize the ads better for traffic.
Another stupid advice.
Go to a buzzfeed.com - tell me what ads do you see? About jokes? About gifs? About meme? No, you see ads that are targeted to you based on your previous browsing history, interests, behavior. The ads that you see may target you specifically by your location, salary, education level, or even targeted by IP.
When advertiser sets an ad campaign most of the time he doesn’t care where the ad will be shown, he target specific audience. Additionally he target how many times this ads should be shown to specific user. So, no matter what site are you on you will see specific ad certain amount of times.
There are such things as a whitelisted and blacklists, those are options that allow you to block certain sites (like TMZ) or to show ads on a certain sites, or block specific list of IPs to prevent showing ads for nothing.
So as a publisher you’re making a big mistake and loosing a lot of high paying inventory if you’re blocking mortgage ads on the site about cats. That is simply not clever.
The whole point is not to increase CTR, but to create a quality content that will attract quality traffic. Quality traffic attracts quality ads and prime advertisers. This is how you make money.
There are such things as ad server and headerbidding (also uses ad server) where you set multiple ad networks instead of one. The purpose of both solutions is to increase publisher monetization by using multiple ad networks instead of one and making them compete with each other. When ad networks compete - highest bid wins, so how would they compete if you block all advertisers? Again, I don’t think you have big experience on traffic arbitrage.
I get your point - if you have site about cats, and let’s assume it’s popular, then you can make a lot of sales of cats food (doesn’t always work like that), but in this case, you will set cat food advertisers as direct advertisers and their bids would be way higher $20-$100 CPM. But you don’t use Adsense for that, those are direct deals or specific ad networks that represent advertisers on direct deals. Those direct ads are also through an ad server and compete with other ad networks. In other words you don’t block anyone to make more money, but instead add more.
My CTR is perfect, it’s not the CTR you should worry about. CTR is work of the advertiser, not your content, not your theme can affect that. The only thing that can affect it - ad placement.