If it’s TBC, wrath or cata timewalking you can do the weekly in the associated timewalking raid (which drops gear equivalent to normal raid loot) without having to do any 5 man dungeons. Those weeks also have a weekly quest for a piece of heroic equivalent loot. Which is a little better.
But overall I get your point.
Outside of farming badges for cosmetics (the gear from the vendors is useless for alts as they currently 541 while quest blues from azjkahet are higher item level, they aren’t really for max level toons, they are really just for leveling alts, since timewalking dungeons gives more EXP than a level appropriate LFD dungeon does.
EDIT
Timewalking dungeons are getting a change in the future to scale UP to your level rather than you scaling down. Which will make them harder.