It’s in most countries’ political interests to increase their populations, if they can feed them.

Not really. You have one vote in the council per country. For it to be a majority you need both the number of countries >55% and the amount of population >65%. Population is defined as people with "usual residence"in the country. I can't find clarity on this right now but eg refugees would normally not be included. So it's really long term population increase which is rather rare in Europe.

With 83 million people Germany has 16.18% of EU residents (18.5% post Brexit). Adding 1 million increases the weight by around ~.18% (or ~.23% post Brexit) - assuming you get people from outside the EU and thus an overall EU population increase. Thinking strategically, you could think this matters if this is a long term trend. But factually you have to have quite a lot of shifting population (within-EU migration) to change the set of possible alliances that can reach 65%.

Moreover, even the smallest country retains their individual voting weight, so if one country grew so big to overshadow all others they could still reign it in through majority vote.

And then split into multiple smaller countries in order to get better vote per capita ratios.

Of course, an expert conspiracy theorist will note that the more or less culturally and linguistically homogeneous group of about twenty million people living in the north of Europe are already split into a vote-buffing four countries ...