Most medieval food actually used multiple flavors, seasoning, and mixes of sweet and savory. Sauces like barbecue that involve complex flavors are some of the last remnants of medieval cooking in the European tradition.
The relatively “flavorless” cuisines of European cooking today which focus on intensifying the “natural” flavors of meat, cream, etc, were a reaction to the point where spices became so affordable it was impossible to show off with them; the rich retaliated by choosing a new way of showing off which focused on pure, extremely high quality ingredients and extremely intensive labor that the poor couldn’t replicate. (Eg. Sauces that require hours of constant attention are unattainable at home for anyone who doesn’t have servants.)
If all of your cooking is from a Western European tradition, your daily food has significantly less flavor than a peasant’s in the 1400s’.
(in terms of sources, would recommend checking out ‘consider the fork’ [wilson, 2013])
this does not seem to counterindicate the thesis of the tweet, since he was talking about peasants
peasants used flavors. they used flavors so popularly that there came a point where no quantity or kind of exotic* spice was enough to distinguish the rich from them. before that point, they used cheaper and local flavors/lesser quantities. (eg. there are plenty of herbs that grow in Europe.)
again, if you want specifics I suggest you look up medieval cookbooks. Some are rich people’s recipes but not all are, and they’ll give you a lot more specifics and a sense of the different way we thought about flavor in the middle ages, which is a lot of what makes the above tweet laughable.
*here meaning imported at considerable expense