Gladiators Were Vegan

Gladiators were slaves, and very expendable ones at that. Of course they would not eat much meat. Romans did not feed slaves meat or any high-cost foods. Its only Hollywood that makes us think that gladiators were some kind of UFC supermen athletes.

Roman soldiers did eat meat, cheese, and considerable amounts of olive oil, as well as a solid diet of various grains. Of course, they ate whatever they could get at the time too given the difficulty in preserving food and maintaining supply chains. You can read this book and look up "meat" which references lots of dig sites of Roman camps with animal bones in addition to literary references to the typical rations of a soldier.
https://books.google.com/books?id=LfRiXN5hhCUC&lpg=PA27&ots=vzuB41Yu2j

I see no reference about Roman soldiers not wanting to eat meat before a battle. But that said, eating any heavy meal right before hours (or days) of significant physical exertion is never a good idea. A chunk of meat is clearly not a power food you'd eat before a battle... and really I don't think anyone would argue against that!

The idea of desiring a meat-free diet is a modern idea. In most cultures such a diet was reserved for the very poor. There are many benefits to eating a whole food, plant based diets. But doing so does not bestow super powers or strength nor even superior athletic abilities compared to athletes who eat other diets. Athletes who are vegan/vegetarian have to be incredibly particular in balancing their nutrition and usually are loading up on high protein plant sources (quinoa, soy, legumes, etc). That's great that it works for them. Most vegetarians I know are not bulky though but are rather quite lean, which is one benefit of that kind of diet.

When I moved from a low-fat, plant diet to a high fat diet with eggs, cheese, raw milk, bone broth (ie: chicken soup), and butter as well as plenty of veggies and grains, I put on more muscle. Some people's bodies work differently. I know how mine works.