perfect or harmful use of h2 tags?

hi guys!
I noticed a trend in some websites that do SEO

they would use a keyword or a variation of it inside h1, h3 and h4 tags.
I know this is great for seo! but they usually have two h2 tags, and from 5 to 10 h2 tags and a couple of h3 tags on each article, and every tag has a keyword or a long tail keyword in it.

is this practice normal or safe for a long term website?

It is safe, just you need to maintain the format.
But yes, don't use much H1 tags

You should only have one H1 on every page of your site.
H2 to H5 are used to help the user/google understand the hierarchy of your content, and what's in it.
You should never underestimate the power of Hn.