Not necessarily. It's not actually clear what they mean when they say the "leading" product, although the more likely definition is "the one with the most sales". Many products (at least in Britain) will be advertised as being "more X than the leading brand".
PS: "I bought a packet of floss/some floss, and it had/has this sentence on the back"
"Does the leading floss mean best (floss) available (floss) on the market
flossin this context?" ("Floss" can go in either of the places I put, but not the one you did)
[Not a teacher]