For a representative fast growing B2B play take a look at Cisco in the 1980s through 1990s.
Some B2B plays are easier and lower entry costs than the corresponding B2C plays. For instance there are only a dozen or so manufacturers of dentures. It is trivial to build a lead database of all of them, and to call or visit I every one of them. if you had a new material for the appliances.
These manufacturers supply the entire dental market of a few 10s of thousands of dentists. A B2B SMB play could buy a list (since dentists are licensed) and do telesales to all of them for a few dollars a piece.
Millions of people will visit dentists this year. But only a small percent will need new dentures. You may have to advertise to millions just do discover a significant portion of your target segment so your cost per lead can be high and efficiency low. So building a consumer brand in this space can be much harder.