As far as I've tested, it happens on realms. Given that it was on realms and the better together update has been released, I believe it can be replicated on all better together enabled platforms.

I was full HP wearing full iron armor, also at full hp, and one fireball from a blaze breaks the armor and kills me in one shot. If it matters, it was done on normal difficulty.

If anyone needs any help replicating me a dm on twitter @smol_doggos

Thanks.