With the buffalo argument, a lot of people are trying to compare the buffalo MKII (a freighter with some missiles strapped on, civilians/pirates cooked up because they had nothing better to stick the missiles to) against specialist role combat warships.
Its like comparing a caravan some hillbilly survivalist modded and stuck a hatch on top with a couple of AK's and comparing it with a hum-vee and a challenger 2 main battle tank.
Yes it has no reason to be in a hand picked fleet, just as you wont find retooled caravans in an armies main lines (unless that army is a ragtag force using dregs and cobbled together trash), But those caravans would exist in a post collapse mad max scenario, sure tanks are better, but how many hillbillies can get their hands on tanks?
The buffalo MkII has a role In universe and in lore, being what desperate people make do with, when they only have hope, spit, and grandad's left over Pilums. When the campaign is properly fleshed out, don't expect to see these in any organised military fleet, but DO expect to seem them in the hands of pirates, small merc factions, and the odd small independent station/colony's defensive "fleet"