https://playoverwatch.com/en-us/career/pc/Fareeha-1186
https://playoverwatch.com/en-us/career/pc/Valkia-2299
% Direct Hits on 2 of the best pharah players around are ~20 percent.
So that means 1 out of 5 hits are direct
Their average highest potential damage is around 88 per shot with the 100% hits of old splash.
New splash of 65 it is 76.
A relative reduction of 16 percent. 88 to 76
With the increase rate of fire of 20%. 0.9 to 0.75
Total damage has almost no change over time, provided that the direct hit accuracy stays the same and you are fully taking advantage of the increased fire rate.
The burst damage as already mentioned if on average only 1 hit is direct out of 5, there is a lot of lost up front damage that we had with pharah.
If a 200 hp hero could be killed in 2 shots, 120 + 80 before, but now takes at least 3, and since the person could be healed between shots, there’s a chance it will take 4 or you may not even kill the hero.
Assuming, direct hits go up with pharah play style changes (flank/short range), it could be a buff provided that survivability is unchanged or better in the new role.
TLDR: the best pharah players average 20 to 25 percent direct hit rate. With this information, we can extrapolate that the damage appears to be wash in regards to damage over time average. It shows a significant loss of burst potential to break points that traditionally would kill a 200 hp hero.
Edit: found this thread in general - similar deduction: