Well, as far as I have been investigating, Stormbow + Holy arrows combo is about 50% nerf on average, using both the DPS meter and kill times of various bosses (statistically 28% from bow, and practically 30% from arrows? they are multiplicative by the way, so it does form 50% total). That's a lot lower of a hit than proposed 75%.
Of course, in ideal case scenario which is coiling Destroyer (he guarantees all the piercing stars will hit), arrows themselves suffer 60+% nerf (halved hits of stars, halved damage of stars + defense affecting low damage more), so said Destroyer now dies as long as other mechs from that bow, that's a definite improvement from 1.3 situation.
However, on single target, especially big one like bosses, piercing meant close to nothing but also capped the amount of stars that will land hits to 6/s or lower. For reference, currently Stormbow produces up to 19 (!) stars per second. Even considering a lot of them will miss the initial target, it's still a boost to single target performance nonetheless. Minor detail to mention is that those stars usually come in same bursts as arrows do, so missing a few barrages will still net a similar ratio between "nerfed" and original states.
Do I want Stormbow to be nerfed even more into the ground? Probably not. Do I prefer if there was more field to weapons other than Stormbow in ""competitive"" gameplay? Indeed.
It hurts to say but probably that bow has to become a bit less friendly to use in order to keep that insane power. Maybe no autofire (although clicking out feels terrible on most weapons), perhaps a charged shot (albeit that's way too far from what that thread can achieve), possibly a lot lower firerate but higher damage to compensate (so every shot is impactful but also has to be managed carefully). Something to make it not a spray-and-pray melter.