i'm not sure about the reason behind all those preemptive kicking i had encountered, probably because i'm only HR14 (low ranking because i started late last month, played on and off along with other hobbies and due to work) and my total usage of hunting horn isn't even reaching 100 (that's also total quests and investigations i done so far); as for those kicks happened in rooms hosted by hunters whose rank is lower than me, probably due to my sub par defense (lv4 pink rathian beta set, about 300 def)?
so far i'd only managed to party twice (with friend who had concern of me with zora, then later nergi fights) and often times i feel reluctant to join other people's room (once being in a room full of ang-mohs but no one taking any quests, and the rest were just kicks).
from what i discovered from using hunting horn is the increase attack output and move fluency compared to previous mh series. the buffing move still locks player up with animation, but kaput-con added hunting horn to trigger additional damage (and exhaust/ stun?) during buff, if the horn is close to the monster. the complain about hunting horn having slow attack speed (and long swing animation) is actually offset by it's reach and wide swings. also, it's the 2nd weapon which won't bounce when hitting hard points (first one being hammer)
comes to think of it, the kicks i experienced probably be attributed to hunting horn's wide swing arc and the hunting horn pound? but that would mostly contributed to bad positioning (and from experience, 80% would just do their combos at places where better suited by hammer/ hunting horn/ lance/ gunlance, which is head area), plus for other players tripping them off their combos are always bad but everything is fine when they trip other players
** note: i mostly main hammer in other series, except for mh3g where i spent time using lance and with mhw where i exclusively use hunting horn...
Likely coz you're low rank. Never experienced HH users being kicked before and I played most with HR 100+ now. Like some said mostly soloed until I hit at least HR 50 but have the occasional multiplayer back when game first came out.