Yeah, they definitely changed something.
Last Timewalking event was MoP Timewalking and it ran from
30th April 2019 to 7th of May 2019, literally ended a few weeks back and timewalking dungeons were giving between 460,000 - 620,000 XP depending on heirlooms and if you had an exp pot etc…
this new event that just started for WoD Timewalking, it’s giving like 250,000 xp per run maybe, i only did 1 run to test it out but i didn’t get exact numbers.
Last event i leveled 3 toons from 110 - 120 and it took about 22 timewalking dungeon runs… either it’s nerfed or bugged but it’s nowhere near as good as it was