Nettle is a h2 blocker, so that makes sense for your mcas. I have only take peppermint tea myself, which is a h1 anti histamine. It also reduced swelling in my throat due to the menthol.
I did try to get nettle tea but was not successful
I also found out rosehip tea has the best anti bacterial action for throat infections.
So all I know is your thinking is sound, it should help calm down your mcas and I personally take the Solgar Quercitin capsules when I am having a weird flare up it definitely calms down an all body allergic reaction - which is very similar to an MCAS reaction.