Once you sell a share you don't get to control who it is sold to afterwards, you could give shares to people as stock-options, and they are (rightly) going to sell their shares regardless who the buyer is, only based on the price.
So. Seriously, shut the fuck up, you're suggesting that the only answer is isolationism.
Identification of an issue (people buying up European talent before it gets large enough to be competitive) is not an invitation for absurd and deficiently reasoned victim blaming.
If you want to keep control of a company - or anything - within certain hands, then you can't sell that thing to others. As evident by millions of companies never having their shares publicly listed or sold on any market. If you sell, you have to accept that you don't have any control of who owns in the future. You can't have your cake and eat it. Not even Europeans can do that.
"People buying up European talent" - they can only buy if Europeans are willing to sell. Such victims...
This reminds me of people complaining about foreign investors buying up real estate. But of course, no blame is to be put on the greedy sellers who slurped up that juicy foreign money.
Nobody can force you to sell your shares. Nobody can force you to make your company public. It's all voluntary. You can't have your cake and eat it. Want to get that juicy foreign investor money then cry that the foreigners are taking over?