I'm not sure why you think such a company needs to exist. Almost all apps run fine on my Samsung Galaxy S5, except for anything made by Google or Samsung. With Samsung I think their software engineering is incompetent, but I think with Google there's probably a lot of pressure to "just make it work" that the engineers mostly test on the latest and greatest Android. Plus I'm sure there's an unspoken rule not to allow older phones to be too useful for too long.