Herbivores have digestive tracks that are better at breaking down plant matter than ours [1]. They also spend far more time eating [2]. Obviously these are not huge problems these days, since we can grow plants that give us more protein and calories, while being easier to digest. But to say "hippo get strong from eating plant, you get strong from eating plant" is pretty silly. If you spend 5-6 hours a day eating grass like a hippo, you will die from starvation.
Hippos have to graze up to 16 hours a day. Meat is a shortcut that enabled our species to put time into other things that made us the dominant species on the planet.
The claim is that meat is "essential" to become big and strong. Which nutrients in meat are "essential" for this but not in a vegan's diet, so that they have to fill the gap with supplements to be competitive in sports?
For what one anecdote is worth, I'm friends with a former professional athlete who tried a vegan diet after after retiring - and years on he is still as freakishly strong and agile as ever. Many well-known pro athletes have gone vegan during their careers as well: Chris Paul, Venus Williams, Carl Lewis, among others.
1. https://stluciasouthafrica.com/hippo-facts/hippo-digestive-s...
2. https://ielc.libguides.com/sdzg/factsheets/hippopotamus/diet....