Never found, nor tested a difference in making a divot in the bed, I have done it in the past. I think that was a fairly recent fad, one of those things that gets re-discovered and pops up over & over in cycles.
You’re going to stir up the bed when you brew, you can’t distribute the grinds and keep them in place like in an espresso puck.
Nobody really tests effects on taste. It’s too complex a thing to do and most of it is decided before you start brewing, when you purchase the beans.
You’re not reducing agitation, you’re just not increasing it. The water being poured is usually enough to wet & separate the grinds, excessive agitation only makes cups more silty/powdery/bitter. I’d only agitate/stir early on if grinding/brewing very fine and you want to be sure of getting the dose properly wet at the start (not something I do with a gooseneck kettle).
Don’t understand continuing questions about temp in the kettle. I use an electric kettle which clicks off boil & has to cool some before I can click it back on, so I can’t test this. Difficult if pouring every 30 or 40s. If you are heating on a hob, then the kettle will hold some heat as will the remaining water. If you can over-extract coffee when brewing with boiling water, with no continued heating, how much more heat do you need?