One of the major variables in making tea or coffee is the temperature of the water you use. There's quite a bit of contention regarding what ranges of temperature are appropriate for different kinds of each.
In the case of coffee, there is mostly broad agreement that the lighter the roast is, the hotter you should brew, with many experts saying to use water that is fresh off of boil for light roast coffees.
For tea, generally folks agree that hotter temps should be used for black tea and while many suggest lower temps for green teas. Oolong is all over the place both due to differences in how folks brew and because the actual process of oolong includes teas that are basically green teas and teas that are basically black teas as well as much in between. White tea best practices also seem unclear (although the common received wisdom to brew at very low temps seems to be wrong), because white teas are not "fixed" in production, meaning they age much more rapidly than other teas. So some need to be brewed very hot, others not so much.
The other factor that is extremely under-scrutinized is the difference between the nominal temperature of the water you're using at the kettle and the actual temperature of the steeping beverage in its brewing device. What you brew in, whether and how you preheat it, and how you pour into it will all change the temperature at which the extraction is taking place. You can measure your brewing temp, and it's not hard to if your brewer has an opening at least large enough to fit a food thermometer into, but few experts actually give advice regarding what that temp should be, except in the realm specifically of espresso.
I currently don't have a variable temp kettle, I actually have a Zojirushi water boiler, which is incredibly convenient and I love it, but it's actually kind of a pain in the ass if you want water to be boiling hot. It has several temperature settings, the highest of which is 208F/98C, but that's the temp in the boiler. After passing through the pump and being dispensed, it's more like 93-95C, and if my brewing method requires either weighing my water or using multiple pours (such as in gongfu tea or pourover coffee) then I must decant from the Zojirushi to another vessel. A vacuum insulated bottle does a pretty good job of keeping the water almost at the same temperature it emerges from the Zojirushi at, though. So, most of my tea ends up getting brewed at around 94C purely for reasons of convenience.
To get to a higher temperature, I can "temperature surf" by using the reboil function, watching the temp display and grabbing the water when it reads boiling. But even using this method it's hard to get the slurry temp of brewing coffee (in a preheated plastic pourover brewer) above 91-92C. But it is still definitely faster than waiting for a kettle to boil, so I'm not planning to replace it with a fancy pouring kettle.