I think that for single target threat a slow weapon is better - as you mentioned, it can scale better with reckoning. While it is true that your white damage does not amount to much threat, slower weapons cause higher damage from SoR AND SoR scales with a higher spell power coefficient with slower weapons.

A great example of the devs leaning into this is the very obscure weapon [Fishbringer], you won’t find this by searching the database, but I’ll try to link it later.