Tier list putting Reapers Crest there is questionable.
Compare Reaper Crest to Wanderer Crest. Wanderer lets you attack more than 50% faster, which means, during boss fights, you will generate 50% more silk and deal 50% more damage in the longer form interactions. Simply for using a different crest.
While the Reaper Crest markets itself as the "You'll get a lot of silk after binding" crest, you can do the same thing (without chasing down the silk orbs) by just using the S tier Wanderer Crest.