Sounds like you're dealing with sleazy dirtbag black-hat SEO bullshitters. People who CLAIM to understand SEO but all they know are goof-assed tricks guaranteed to get you kicked OFF of search.
If you are choosing your HTML for "SEO reasons" you're using HTML just as incorrectly as HTML 3.2 style presentational markup. Remember the advice Matt Cutts gave us over a decade ago in regards to SEO:
"Write for the user, not the search engine"
And writing for the user means proper semantics, logical document structure, and telling those peddling goofball tricks and abuse of headings to sod off.ABUSING
H1 for SEO ranking purposes is broken nonsense more likely to get you pimp slapped off of search in the long term. Because it's an accessibility violation. BECAUSE you aren't establishing an accessible document structure. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Heading_Elements#accessibility_concerns
h1 (singular) is THE (singular) heading (singular) that everything
on every page of your site is a subsection. That's what it's FOR. Just as an H2 marks the start of a major subsection where the first H2 (unless you're using MAIN) is the start of your main content. H3 marks the start of subsections of the H2 preceding it. H4 marks the start of subsections of the H3 preceding it. Do I have to explain H5 and H6?
Think of the H1 like the title of a book or newspaper. It might have different appearances across pages, but there's a reason it's at the top of every fold-pair.
Choosing them JUST for SEO reasons is a sure-fire indicator you're dealing with someone not qualified to open their yap on the bloody subject!
Sadly far too common a situation with the sleazy dirtbags claiming to know about SEO, lazy dirtbags using gibberish bloated scam artist rubbish like frameworks, etc, etc.
I deal with ignorant know-nothing quacks, morons, and fools who spew gibberish about "h1 for search" all the time. You kick them in the groin and say "no, that's not how this works. That's not how ANY of this works".
What they think is "SEO" is nothing more than dumping a can of shellac on a pile. It might be shiny, but it's still just bug excrement on horse manure. Sleazy, disreputable trickery to try to cover up for bad copywriting skills and a general lack of "content of value".
It's why I'm such an advocate of content first development, of using HTML to mark things up to say what they are, NOT what some SEO turd says or what things are supposed to look like. Why? Because in the long term it works BETTER for SEO than their entire bag of trickery and chicanery.