The difference it’s about quality of life, nothing else, having a lvl 6 Healing Factor is enough for it to have 100% uptime, you can reach that with Divine Might but I prefer to have it already that lvl so I don’t have to cast it everytime I want to use Healing Factor, more lvls into it it’s more of a personal opinion and when you literally have nowhere else where you’d want to spend your points into.
In my case I only have Incineration lvl 5 because I’m a full SPR Chap-PD2 so the scaling is not that good (it’s already not that good in the skill itself to begin with), however for an INT build you’d benefit more from lvling it because you can actually improve it’s DMG more because you’re using INT on top of your Transmit Prana which makes it hit even harder if I’m not mistaken.
I always prefer to have Bloodletting maxed because it’s utility it’s really good, at max lvl and Divine Might it has 100% uptime so that’s 1 min loop where you’re inmune to debuffs which I find to be awesome in some scenarios, maybe in PvE doesn’t have that much of an application but there’s still some mobs out there that apply nasty stuff to you (like the SP Drain from some mobs, I’ve find that Bloodletting nullifies that nasty thing and I don’t get my SP drained).
So yeah, lvl 5 is enough for Healing Factor as you can make it have 100% uptime with Divine Might, lvl it up to 6 if you don’t want to cast Divine Might everytime you want to use Healing Factor and going beyond lvl 6 it’s only when you don’t have anywhere else you’d want to spend your points into.