Lack of H1 / h2, etc. - how much does it affect SEO?

Question

Search Engine Optimization

I've seen sites that don't exist at all. But they rank pretty well. How critical is it if the site does not have these tags? And is it possible to do something so that under this condition the damage to SEO is minimal?
And yet, how bad is it if, for example, paragraphs do not go in solid text
Not so

<p>Первое предложение. Второе предложение. Третье предложение</p>

let's say it's like this.

<p>Первое предложение</p>
<p>Второе предложение</p>
<p>Третье предложение</p>

Answer 1

Indexing will be worse (since googlebot or yandexbot will understand the structure of the site worse)
You can embed keywords in h1 headings, etc.
From a UX perspective, properly configured headings help users navigate.
It is also worth marking up headings using micro-markup (at least h1)
Compare with competitors, if they do not have this, do it, it will be better
What will happen if you do not use h1, h2 headings?

Answer 2

Google does not count only the H1 / H2 etc tags while calculating over all ranking in fact there are several other metrics and stuff when it comes on counting it on. As an SEO campaigner at NursingEssays.CO.UK I would say that you probably notice only the absence of those header tags but you may have ignored other factors like trustworthiness, crawl budget and strong domain profile where it performs good.