Cutting some corners here - I am a vegetarian, but I can’t remember the last vegetarian restaurant I’ve been to or when that was. It’s been many, many years.
I also do cook omnivorously, just leaving out the meat in my food.
That being said, I agree with Snowboarder Bo’s assessment of your thesis. I’ve been to a number of omnivore restaurants where it seems like chefs have no idea what to do with vegetables and treat them as filler. A lot seem content to just mix up some pasta and marinara, or make a vegetable sandwich/portobello mushroom burger (the latter of which are inevitably poorly constructed/cooked so that they drip everywhere and spatter your clothes), and figure that’s “good enough.” Well, at least it’s not lettuce in a bowl, but it’s unimaginative and often barely flavorful. It’s at the point where I’m almost happy when someone can make a non-soggy sandwich.
Also, many omnivorous cooks are stuck on the idea that you need meat of some kind. I’ve had some put meat of some kind, usually meat-based broths, into my food because they think it’s required for me to be healthy.
Worst homecooked meal was by a non-vegetarian, same with best if you don’t count my cooking - I don’t eat at a lot of vegetarians’ homes as I don’t know many who live near me.
Worst restaurant meal: barely-cooked or uncooked vegetables on a plate, plain. Like slabs of carrot and zucchini, that kind of thing. Seriously. I was at a fancy private club for an event, and either the event booker on my end didn’t say anything until we got there, or the kitchen forgot, or something. At least, that’s the only gracious explanation I can come up with.
I have had some awesome vegetarian meals at omnivorous restaurants - Rick Bayless’ Frontera Grill and Paul Virant’s Vie, both Chicago-area restaurants, are examples of ones that have done amazing things with vegetarian food. I also went to a meal recently at the Tap House in the Chicago burbs where it was a beer pairing event, with reps from the New Belgium Brewing Company and the restaurant’s chef (Todd Davies), presenting a multicourse tasting meal and each course paired with a different beer from the brewery. The chef makes a special meal for vegetarians at these events, and from my husband’s opinion (who had the meat version of the meal and ate little bites of mine), he often liked the vegetarian options better. They were absolutely delicious to the point where I was literally gleeful throughout the whole meal and gushed my praise to the chef when he came around to our table.