How should burger patties be prepared in terms of mixing and flavourings?

There's no right or wrong answer as there are advantages to both and it's about what you want out of a burger.

The advantage of the minimal disturbance method is that the strands of the meat give the burger structural strength. It also gives a pure beef flavor as you aren't adding anything to it. The mix up method breaks up the strands of meat which come out of the grinder which makes patties more fragile, however flavorings are distributed evenly.

Some people add binding agents like egg and breadcrumbs to hold it together when using the mix up method in which case it becomes more of a flat meatball than a burger.

My personal preference is the minimal disturbance method as it is fast, the patties hold together, and I like the flavor of pure beef. After forming the patties I salt them on both sides. After the final flip I grind fresh pepper on the cooked side - pepper gets bitter when burned. If I did want to add flavorings I would grind my own meat for the burgers and add the flavorings then.

Neither is right nor wrong, it simply depends on what you are trying to accomplish.

The way I make a basic burger is to try and pull off the right amount of ground meat from the package and shape it right there as is without kneading it at all. Literally just enough handling to shape it.

However sometimes I want a seasoned burger, and that's more like making a patty shaped meatball and you can't really avoid mixing/kneading it in the case.

Sometimes seasoning the outside of the burger is all that's needed.

From a traditionalist perspective, Kenji is right.

I didn't click through to the Ramsay video, but from your description of him adding lots of stuff, and mushing it up, his burger could more accurately be called "Salisbury Steak on a Bun." Not that that is a bad idea.