We don't need to assume. We have decades of experience and data showing that mobile operators will jam phones full of as much spyware, adware, and experience-ruining garbage as they are legally and technically able.
Yeah, this is basically why Android One, Pixel & Nexus phones, and phones with “Stock Android” we’re/are so popular among tech people because they didn’t come with the carrier or OEM forced uninstallable crapware.