> No idea if mining pools or the stratum protocol has added countermeasures to prevent such an attack in the future.

Not really. There's some discussion about Stratum2 having stronger authentication, and systems like BetterHash to take away a lot of the centralizing impacts of pools by having people create their own work, and only centralizing the payouts for that work. It's a bit of a challenge because there's such a huge range of hardware out there with incomplete implementations of stratum in closed source forks of mining software. You basically have to wait for it to just be obsolete and replaced because there will never be updates.