Yeah, it boils down to preference. Either option is going to work (although Tefnut build takes more effort to beat Arka IV build obviously). I occasionally overheal a target anyways and don't see the maximum amount my cures even do. Admitedly I'm more paranoid in VW when my DDs can be oneshotted and temps ensure MP is near infinite (as long as they're properly replenished, anyway). 1.5 skill bonus isn't something I'd factor as noticeable enough to completely justify the change (given the potential costs involved).

Light weather isn't something I'd honestly factor either unless you're doing Nyzul on WHM or something since it's always active there, or once Limbus gets renewed and Temenos gets additions.

/does listings for lightsday/light weather for personal reference:
Staff +50% Potency, +88-16 Healing Magic Skill, +30+3 MND becomes:
+50% potency, +72 skill, +33 MND.
Tefnut/Genbu set: 50% potency, +83 skill, +43 MND -19 skill becomes:
+50% potency, +64 skill, +43 MND.

And then it's down to 8 skill vs. 10 MND again.

tl;dr: We agree, but I do tend to ramble. lol I also can't justify carrying more gear for such a minimal impact. It's reasons like that that I'd also be carrying an Arka IV build around, and in my reasoning, guess it boils down to keeping it simple.