Links from which type of sites will effect the SERP's!!

[mandiradebnath]

It is not really useless. Till now, blog commenting gives a quality backlink from a high traffic site. It is true that the responses are less, but still there are blog sites who allows guest blog (sponsored blog also). Because a blog from other person also enriches his own site content. I share my content (publish article)  with third party sites and also get SEO benefits for that.

You might get some traffic out of them which is also highly unlikely. But that's it no help from commenting at all.

And think of yourself this. 99% of the blogs provide no-follow links so they are a no help anyway, and the least amount of blog's who do provide a do-follow link they passes no link juice whatsoever.

You have also given the answer to your query. I agree with you partially not fully. Not all site give dofollow links but some give. See this blog  - https://ezinestack.com/mobile-phone-buying-guide-without-credit-card/
And https://deals.megamobiledeals.com/ has published their guest blog here and it is dofollow link. 
We have seen the varieties for dofollow and nofollow links from tried party sites. There are several forums also who provide nofollow link with some provides do-follow links. But all time we should not focus on dofollow or nofollow. We must consider the traffic of that third party sites.