I'm definitely much more fine with damage nulling, yeah. I would consider that a fair challenge; having them ABSORB it is just stupid (though not entirely unforgivable-- at least ones like Awoken Parvati are just boring and grindy), and giving the player a timer until they die is completely unfair.
And yeah Vishnu is definitely a slap in the face for tanky teams, but not as much as he used to be because atk multipliers for tank teams have been getting way better, as are burst options (pretty much every burst active in the common meta has only improved with time, look at Norse gods, Durga, Lu Bu, the Armored Knights, the Gemstone Princesses, etc-- and the fact that stall teams can happily make the best of them as assists). But I also feel like he isn't as overused in dungeons either? Like yeah, he's been used in a few prominent ones, but it almost feels like they throw Awoken Sopdet in any time they want to artificially make a dungeon harder for the units that they insist on making absurdly strong.
Like, I don't know when we needed multipliers of 300x+, but they became more necessary when they start making bosses with like 100mil+ HP, too. I have to wonder if this is just how the endgame is going to keep going. Stronger and stronger stuff at higher and higher costs to take on bosses that.... will still happily oneshot you just because they can.