Bruh LT is the rune of choice when facing bruisers and tanks which is the majority of the top lane matchups.

That said, the section where this guide says "Kayle deals magic and true damage" is misleading since the only source of true damage I found in this page was the elixir. She's a hybrid carry which can be leaned towards AD, towards on-hit, OR can be built as a serviceable burst AP carry. Kayle does not have any form of true damage dealing in her kit nor do the items (shadowflame included, read carefully).

The fun side of LoL is being able to have different gameplay styles, and even having to swap a damage rune for a sustain rune, that's not wrong. The use of berserkers is much better in my play style, where I seek to farm at the beginning of the game, and not exchange damage in the lane phase. And Lethal Tempo is an excellent rune for Kayle, since her biggest damage comes from AA. Finally, Doran's Ring is an excellent item because I can use my Q and W more times before using B. Keyle is a champion who must survive the early game, farm and not give up kills to the enemy. You don't necessarily need an item that gives you more damage in trades.