Gotta say I don't like this change. I've yet to get this mod and use it, but this change effectively neuters any -Mag Cap. + Reload speed Riven builds on pistols, especially ones with a slow fire-rate.
And the wording should generally be "no longer applies to Pistols with < 5 rounds in a Magazine" Otherwise it could be interpreted as: "no longer applies to pistols with less than 5 reserve magazines", indicating a link to ammo pool, instead of magazine size. Unless that's what it is and it isn't linked to rounds in a magazine?