My experience has been that installing AdGuard on my iPhone made no noticeable difference. To be fair, I barely browse on my phone. Basically only news sites and Reddit/HN. But apart from HN I see ads on all of those pages.
So I am just a puzzled by your point of view :) May I ask which App you are using? I would love to be proven wrong and have an ad-free browsing experience in the future.