But if you have a Samsung then good luck loading anything custom onto the device. The likes of AT&T and Verizon have made sure of that through locked boot loaders, eFuses, and things like Samsung Knox all of which prevent you from doing the things you're talking about. It's almost like a Samsung device is locked down just as badly as an iPhone is except that the iPhone actually gets timely updates and Samsung doesn't.
As for updates I mean that a two or three year old Samsung device should be running Android Oreo. There's no technical reason why it isn't, they just don't want to put the bloody time into making that happen. They would rather you buy a new device instead.
And as for you loading your own ROM onto it, cool. I congratulate you on that but the majority of people don't have the technical expertise to do that, they rely on their OEM and carrier to do it for them. Why should these people be left with outdated software just because they don't have the technical expertise to do it themselves? They shouldn't, the OEMs should be forced to provide updates. You paid, you gave them your money... where's the customer service that you paid for? It would be like you buying a Ford and them telling you that as soon as you drive the car off the lot you no longer are eligible for service, you're on your own; car buyers wouldn't accept that. Why do we accept that in the smart phone market?