Burn is rarely completely gone from the Modern metagame, due to its power and linear nature
This type of deck loves a little self-mill to get it going, while also having plenty of ramp to be able to recast those cards
Killing an opponent's Seer allows you to draw a card, sure, but by then your opponent has already taken the best card out of your hand, so youll have to evoke that Thoughtseize bug to draw something good enough to replace it
The Tyrant was out of place in Gatecrash , a decidedly non-artifact focused set, and so it flew under the radar for a while before folks realized oh, wait, its incredibly easy to get 20 artifacts under your control in any Eternal format. With two previous encore performances in Commander 2016 and Commander 2019 , Hellkite Tyrants low print run has meant its kept a price tag that fluctuates for years
95% of the time, the triggered ability probably isnt worth a removal spell thats going to be better sent towards Rhystic Study or Smothering Tithe, but once enough cards have been exiled, the risk from rolling a 20 is going to weigh on your opponents