What happens when one of those giant Chinese (or maybe in the future Indian) companies produces, due to economies of scale, something really useful? Stupid example: 7G internet with steady 10GB/s bandwidth. If America bans it, they'll be at a disadvantage compared to the rest of the world. They could try and copy it / help their own companies develop an equivalent (as China did to try and catch up with the US), but then they'd have just done a reversal, going from breaking up their big companies to trying to help them grow big to compete with China.

The further American companies fell behind technogically, the more it would hurt to ban foreign technologies. And the more that large US technology companies were broken up, the slower America would advance technologically. A huge percentage of RND is currently funded by FANG and the like; being somewhat monopoly-like (and having huge economies of scale) is actually what allows them to fund this: in a perfectly competitive market, where margins are razor-thing, nobody has any money to invest in research or moonshots.