The reason Mahdi is not is not an upgrade is because its hella fast. With haste capped, as it usually is between GoE and /s 2 and bard songs (if the fight allows it) you want the slower bow, for the bigger hits and crits. The way giantkin works now it MIGHT be a bit bigger benefit to Mahdi, but im pretty sure its about even on that front. Probably gives a bigger % increase in DPS but the same raw amount of DPS between the two bows.
If mahdi is meant to fill the space between ballista and UC/Flarewynd, its a poor choice. Give it the same delay and a slightly higher dmg number, or at least a much closer delay and keep the same better ratio, and you've got yourself a deal.
If mahdi is meant to fill the space between ballista and UC/Flarewynd, its a poor choice. Give it the same delay and a slightly higher dmg number, or at least a much closer delay and keep the same better ratio, and you've got yourself a deal.