I’m certainly no expert but it seems to me if foreign ownership of American land turns into a problem our government can simply reclaim the land in the public interest and pay the previous foreign owners a fair price. Or the government can simply tell the foreign owners to sell the land to an American buyer with the understanding it will be taken from them if they refuse.
You’re probably right. Just because a furner buys property here doesn’t mean the US loses sovereignty. That only occurs with embassies which are considered sovereign areas.