For a single mug microwaves are quicker in America. Potentially even for 2 mugs.
BUT in America kitchen appliances have a power limit (usually) of 1,500W. This is usually higher than a standard microwave (1,000W). And since an electric kettle in America is just a heat source in water, it's very efficient. So if you're regularly heating multiple mugs worth of water, or just boiling water for cooking often, an electric kettle is definitely better. They are also pretty cheap.
Now in Europe and the UK, electric kettles are faster since they can often be around 3,000W or higher. But that doesn't mean American kettles are useless. American kettles a way faster than heating water on the stove. And WAAAY faster than heating water on a gas stove.
Kettle is much more convenient. Microwave is overkill, while a kettle is both a simpler machine and turns itself off when the water boils with no guesswork. It's ergonomically designed for pouring into a cup.
The speed argument is irrelevant, they're both quick enough.
There are very good reasons not to microwave tea, first of all:
I usually find microwaving anything in a mug adds some unpleasant flavour from the mug. Using glass eliminates this, but worth noting.
Microwaving the tea itself will break down some compounds and release more tannins, your tea will be worse.
But even if you're just microwaving the water, the kettle wins (depending on what tea you are brewing). Black tea should be brewed as close as possible to 100°C - when you have a kettle you should pour it just as it comes off the boil, around 90-95°C. By that point the water has actually been boiling for quite a while (at least the water around the element), allowing the rest of it to heat up. It's very difficult to achieve this in a microwave, and dangerous too since you can just end up spraying boiling water around your microwave.
I do not say it is chemically different. I'm saying the tee does not taste the same!
You cannot reduce the whole gustative experience to simply chemically composition but there IS something different.
I don't think anybody seriously thinks that hot H2O can have a different formulation. What, are we postulating the existence of isotopes for molecules now?
I have never seen a thread that is more dangerous to the Special Relationship and I am here. for. it. Brits just sat down to their post-dinner cup of tea and the Muricans just got up from lunch, just raging at each other. Move the nuclear clock one second closer to midnight, please.
Chemically yes, physically no. Microwaved water is more buoyant because it has a heat gradient and rarely boils properly. It tends to get superheated and explode rather than boiling.
This is why tea bags float on top of microwaved water but not boiled water.
I've microwaved water and there is always this foam at the top. Furthermore I think the kettle takes away some of the Particles since mine always has timescales after a few days.
Using a kettle is not just a British thing, it is always a good idea to boil water, let it cool down and then drink, I recently read that it also reduces micro plastics by at least %70