Can you provide evidence that Germany, France, sacrificed their own growth? Unless you know something that I don't, what I see is that you're imagining a zero sum situation which is well known doesn't apply to things like markets. That they underperformed the US isn't not evidence of that. Germany and France underperformed the US in the time period, and in the last 100 years too.
If you don't think Germany and France sacrificed their own growth, what exactly do you think "EU convergence" means?
Convergence doesn't refer to growth rates approaching, but incomes (per capita) appproaching.
It doesn't mean that the richer countries grow slower than otherwise. They might grow the same, or faster.
The claim is something along the lines of:
Without planned convergence: country G grows 2% per year starting from income of 30k/capita and country P grows %1 per year starting from income to 10k/capita. Country P will never approach country G in income/capita.
With planned convergence: country G grows 2% per year starting from income of 30k/capita and country P grows %4 per year starting from income to 10k/capita. The two countries's income per capita will converge.
Economics and counterfactuals are devilishily complicated subjects, but claim isn't complicated.
But some people cannot conceive that some arrangements can be win-win.