Overall I like the quest added in 10.1.5 for timewalking for an extra box for the current timewalking raid and the Turbulent Timeways event in general is a nice motivation to gear up an alt I’ve been meaning to get to.
However, a key thing I’ve noticed while participating in these events is that they are not updated with the current gearing system in mind yet. In fact, the Black temple event seems to even give Azerite! To bring Timewalking dungeons and raids into the modern era they should give crests & flightstones. If alts are doing them to catch-up on gear and the timewalking gear itself can be upgraded using those then I think it makes sense for it to drop from that content too.
At minimum I think whelpling and drake crests should be dropping from the timewalking dungeons and raids. Maybe a wyrm crest from completing the quest to do the raid as well.