I see this quite a bit and it's not really true.
Miasma II - 100 potency instant damage plus 4 ticks of 25 potency damage over time totaling 200 potency per target but only the 100 potency can be spammed. It's effectively 125 potency per cast if spammed (slightly less due to GCD and server tick being not quite equal.) Combined with Shadowflare at 50 potency per tick for 5 ticks it bumps it up to 175 effective potency per tick (again, slightly less due to server tick vs. GCD.)
Art of War - 160 potency instant damage that is 100% spammable.
Art of War is objectively better than Miasma II on its own. The combination of Shadowflare and Miasma II is better than Art of War dps-wise, but only barely and the main advantage to the two old spells being that there's a ticking 75 potency that keeps going if you take a GCD to heal. Miles better they are not, however. When you add in Bane is when it becomes miles better (which frankly was what made Scholars OP in all previous expansions.) That said, I definitely miss the Bane/Miasma/Shadowflare days because it was interesting to play. The actual issue with Art of War (and all healer DPS kits these days) is that it is the only GCD button we press during AoE barring the very occasional GCD heal that needs to go out. Single target adds in Biolysis but that's a single button press once every 30s and it's back to Broil spam. It's boring. We're not asking for a full rotation kit like a DPS or even like a tank, but something more than one spell to spam and one DoT would be nice. Energy Drain sort of helps, but while ideally it gets used as a DPS ability it's often spent on healing instead.
P.S. they already did rename Miasma II: it's called Art of War now. If they brought Miasma II back in some form it would likely just be Art of War with an added DoT and reduced up-front potency.
P.P.S. Art of War isn't that bad compared to the other healer versions. It has more potency (they only do 140) and is instant cast allowing for very easy use of all the oGCD abilities that Scholar has. AST with all of it's oGCDs can only do that for 25% of the time and WHM will always clip oGCDs when Holy spamming even when using their haste buff since it reduces both the cast and recast equally.