Mind you that ‘carrier grade gateways’ will easily set you back multiple thousands dollars. We’re talking Cisco hardware here. I wouldn’t really call the €1.200 gateways ‘carrier grade’, they are just regular commercial grade gateways with added functionality like PoE or integrated LTE modem.
Specs wise, all gateways, or at least the radio boards, follow the Semtech spec and use the same Semtech provided silicon. Some gateways use multiple radio boards (Mtech, Cisco) providing additional capacity, but like @kersing says that isn’t particularly useful in most cases.
A DIY gateway will therefore offer as good as the same RF performance of a carrier grade gateway. Those last ones will however offer extended temperature range, ingress protection, service life guaranty, surge protection (both on RF side as PSU side) etc.