@transformau : This is not quite true. Sure, HBG has that Hame niche, but that's about the only weapon who is used in such a particular way (and not to mention this only matters with the Gravios Gigacannon, rest of the HBGs are not suited for Hame). LBG is often used as a status/elemental gun since you cannot effectively use it any other way, Hame or standard hunt.
I don't see many Daora IGs online, mostly Hazy Casters and Hell Ruin Glaive "Omen" (550 blast is broken yo) with occasional Mind Sticks and relics. As for CBs, most users go for the ultraburst but there some who specializes in guard pointing playstyle (which is just awesome to watch and much more stylish than rushing the burst). GL is about shelling, well that's natural. If you don't shell you might as well play Lance. Shelling deals a set amount of damage regardless of monster part, that's GL's main selling point. That and it's got 3 shell types. Speaking of Lance, some players likes Guard Lancing better, others like me prefer Evade Lancing. SnS can be both a supportive weapon with utility skills to set up traps or AoE healing but can be played as an extremely fast elemental weapon just behind the DBs. DBs users are mostly Demon Dance spammers but some some people like to maximize damage output by risking themselves into Archdemon mode (I think they call that the "slingshot style").
I'm missing out on some other playstyles but there is no such thing as strict as you make it sound like. It's only natural to play by a weapon's strengths. The only weapons you could say are more or less rigid in terms of playstyle are the LS which relies solely on reacting to the monster's every move and dancing around them, GS which is all about timing and knowledge of the monster's moves (though there is also GS-Hame which doesn't work the same way at all), and Hammer which functions similarly to the GS but you're only going for the head.
So yeah saying that everything is only limited to one particular weapon or task is greatly misunderstanding the game.