yes, it's now a good counter and unlike other water Pokemon, it takes neutral damage from solar beam

I noticed the same thing.

When it is ranked by "overall' it's ranking actually *falls* for Es/Solar beam.  It is ranked 5th for SW/Solar Beam after Omastar, Raikou, Zapdos and Dragonite.

It does become the best Entei counter.

Assuming each attacker has its best moveset, Pokebattler ranks Raikou, Zapdos, and Tyranitar still ahead of Gyarados.

With Gyarados getting Waterfall, does Gyarados now get a place among the best counters vs Ho-oh? I know Golem will still be the king due to double SE rockmoves, but I think Gyarados is now a serious candidate for the nr2 spot. Are there any numbers available on this yet?

Question about Ho-oh counters