*I agree that eating before others is rude. Because if you are sitting down to eat together, then you are sharing a meal. If you've already half finished yours before they start, they are going to feel pressure to rush eating theirs, or you are going to be sat looking at an empty plate for a while as they finish.
If you are eating a meal together, then you are eating a meal together.
Eating as a group is a social activity that's more than just about putting calories in your body.*
I disagree. It’s uncomfortable to stare and watch your food get cold waiting for someone else’s to arrive and theirs is hot. I rather others eat while their food is fresh than waiting for mine to arrive. Plus, some people are slow eaters, some are fast eaters, some eat first than talk, or eat and take breaks talking so regardless there will usually be someone finished before everyone else.
I can easily talk and wait instead of expecting everyone to wait for mine while their food gets cold.