What is the correct nesting of links from the main page to IM products?

Question

Search Engine Optimization

We are redesigning the site, discussing its new structure with SEO specialists. Several disagreements and ambiguities arose. I would be grateful for any ideas and suggestions
. On the old site, the main site had a catalog of product categories, the link looked like Main-Category.
On the new site, SEO specialists offer to make a more in-depth catalog - Main - Group - Subgroup Category. They say you need a large nesting, the product cannot be available already at the 3rd level.
For the old site, they suggest doing a 301 redirect or even turning it off - they say the new structure is reindexed itself quickly (there are 6000 products in the store)
Are they right?

Answer 1

I can't speak for seo - but in terms of conversion - the fewer clicks to the product, the better.