I have done some testing on just the mana regeneration part and the status effect as called out and displayed on the tactical menu. This was done solo against Outlaw Enforcers in the Villa in the Hinterlands, as well with an AI-disabled party against the dragon in the Hinterlands. I have the PC version. Here's what I found so far:
- You can't apply Weakened to anything with Guard up. If you had Weakened up before it acquired Guard, it seems like Weakened wears off normally (it doesn't instantly disappear when they put up Guard), but I was not able to test this enough to be sure.
- You can't apply Weakened to anything with Shocked that is not also Asleep. You instead attempt to apply Asleep. This does not consume Shocked. This happens even if the enemy is immune to Asleep and you will NOT get Weakned instead. So: definitely do not apply Shocked to Asleep-immune bosses if you want to maintain Weakened.
- If you use Veilstrike against a Shocked and Asleep enemy, you do get Weakened applied successfully (The other two will wake up the enemy first, causing the Weakened effect to instead re-apply Asleep).
- Weakened applied to Chilled or Burning targets seems to work normally.
- Using Stonefist on an already weakened enemy, you do not appear to get the benefit of Weakened's mana-regeneration for Stonefist itself. It does seem to refresh the mana-regeneration effect.
- Using any Weakened effect while another one is already on the enemy will sometimes this can result in "Weakened" itself dropping off the enemy when the first effect expires while the mana-regeneration effect continues, but it's not consistent. Letting Weakened (or psuedo-Weakened) drop all the way off I was able to apply a new Weakend consistently with no evident cooldown.
So far, it seems that, if there is a bug (with reapplying Weakened) it isn't always consistent and does not seem to affect the mana regeneration. I'd like to know if it affects your character's ability to deal more damage to weakened targets (should be possible to test this fairly easily), and some more clarity on whether the damage reduction to the enemy either from Weakened, or the passive, or both are affected when Weakened drops off during re-apply.
Opinion: I don't feel like this cripples the Rift Mage. My guess is that different player's varying experience applying Weakness to bosses is actually tied to the Shocked->Weakned = Asleep issue. The ability to turn Shocked->Weakened into Asleep is actually very nice. This means the Rift Mage can trigger Shattered, Discharge, Rupture, and Nightmare without any help. Against ordinary enemies, I'd probably prefer to just combo them down quickly. Against bosses, I'd just avoid an Electricity staff and make sure nobody else in the party is applying Shocked (assuming Asleep immunity, of course). It would be nice if they would fix it so it just skipped Asleep and gave you Weakened when the enemy is immune, but that may be hard to do. Also, hopefully they fix the refresh issue so Rift Mages get their full defensive value without having to wait for Weakened to drop repeatedly.