Trying to bust into the HVAC company cartel will be the death of this idea. Most HVAC companies are highly local and have built their business around partnerships with supply houses and the US big-boy manufacturers (e.g. Carrier, Trane, Lennox). The Asian brands (Mitsubishi, Midea, Gree) have taken years to start penetrating the US market, and even then, many have done so through partnerships with the above US brands.
No reputable HVAC company is going to install a 'no name' dotcom branded unit that they won't be able to service with parts from their local supply house. They, and their suppliers, won't be getting the typical kickbacks or be able to mark up the unit costs and they likely won't offer any kind of warranty (at least on labor). To them, this is no different from Joe Homeowner ordering his MrCool/Goodman unit online and expecting them to install and service it for a low hourly fee. It's not worth their time or potential risk when the customer raises a stink a year later when that company reminds them they have zero warranty and parts aren't readily available.
You're insinuating that doing the work yourself means you'll have poor air quality, poor thermostat integration etc. That's not true at all. If you've gone to the trouble to do a DIY install then you're now already experienced enough to install a heat-recovery ventilator to get fresh air into your home via an independent system. I installed my own ecobee thermostat with my heat pump and electric furnace and it works with HomeKit so is integrated with my entire ecosystem.