Reaper is fine IMO. Only caveats the class has is niche Harvest Moon use. Which if you wanted a single target gain in the same time it takes to charge up you can just Harpe 3 times for 900 pot.

It's utilities are Arcane Crest/Circle and requires liberal use of the Death Design debuff to maintain a 10% self damage buff akin to OG DRG Heavy Thrust. Not sure if stacking a truckload of Det boosts your passive damage further to get a permanent 15%-20% increase.

And your burst is primarily during Enshroud phases. So build up 100 Shroud and you can go Unga Bunga with your Shroud Skills, throw out Harvest Moon and 1 Harpe and use Communio and then re-enter Shroud and do the same thing except replace HM with 3 Harpes and if you did this during Arcane Circle you can use PH after your 2nd Communio to get 50 gauge for another Enshroud phase and do your Unga Bunga a 3rd time and you are pumping out a lot of damage in a minute once you build it up.

And the HM and Harpe and possible Death Design attacks should only be used to let the Enshroud recast end it's CD which when that happens you use Communio and re-enter shroud immediately.

TLDR : Reaper damage is primarily Soul Reaver stacks and Enshroud.