Vegan food is bland and boring
Most of the world's great cuisines are built on pulses, grains and vegetables. The complaint usually describes a familiar meal with the meat removed rather than cooking from those traditions.
Meat, cheese, eggs and butter are where much of the savoury depth, richness and satisfaction in cooking comes from, and taking them away leaves food that tastes thin and unfinished however much effort goes into it. People who have actually tried eating vegan, at home and in restaurants, keep running into the same experience: dishes that feel like something is missing, plates of vegetables and grains that never quite add up to a proper meal. Being told this is a matter of perspective does not change the fact that, meal after meal, the food they are offered is less enjoyable than what they gave up.
The experience behind this is usually accurate as far as it goes. A plate constructed as 'the usual dinner, minus the thing at the centre' is genuinely dull, and a lot of early attempts take exactly that form.
It describes a method rather than a category of food. Indian, Ethiopian, Thai, Levantine, Mexican and southern Chinese cooking all have extensive plant-based repertoires developed over centuries: dishes designed from the start around pulses, grains and vegetables rather than adapted from something else. Add to that the techniques that generate savoury depth without animal products: browning, fermentation, miso, dried mushrooms, tomato paste, smoke, acid and salt.
Drawing a general conclusion from a sample too small or too unrepresentative to support it.
How it applies here: Generalises from a narrow sample (usually a few substitute products or a plate of plain vegetables) to the whole of plant-based cooking.
Replacing someone's actual position with a weaker, distorted version, then refuting that instead. The original argument is left untouched.
How it applies here: Treats vegan food as conventional meals with the meat removed, which is not how the cuisines with the deepest plant-based traditions construct a dish.