Raiding Heroics... right. Well, I've just started doing Flex
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--> Wipefest. Not because of the lack of healing on my end, I'm ilvl 530 Holy Pala and healing is fine! I tend to get outhealed by Resto Druids or Shamans at same ilvl or somewhat higher though, but that's normal when I see Raidbot stats. We wipe because ppl don't know that Flex is slightly more difficult than LFR... I can not compensate that with better healing.
I have mixed feelings about Oracle (positive for the most); most of the time I still have plenty of mana or even 100% at the end of a fight. I switched off "Cancel cast" for three reasons:
1: You just heal less if you cancel your casts (not talking about overhealing, but in general; you want to snipe those heals away from your colleagues!). Nobody is interested in overhealing anymore, as long as you don't go OOM.
2: My toon is waving his arms like a mad man multiple times per second when wanting to cast "Divine Light" and cancelling immediately. It does that many times during each boss and I look like an idiot. I don't know if others can see that, I think it's too short to be send to the server but still... It's terrible.
3: Mana is not really an issue anymore; I hardly go OOM.
I'm using Light's Hammer btw; seems to be working really fine for exact placement when needed, but I'm hardly the guy to talk to to get your healing up seeing you're way better geared then I am.
One bug I do have with Oracle. Many times the healing stops completely, not casting anything anymore and my cursor turns into a hand with a blue edge around it. At that moment, my log is spamming that it wants to cast "Holy Shock" on a player but for some reason it can't, so it keeps trying. Sometimes only 5 times, sometimes 10 or more. It stops doing that when a higher priority spell is needed or when I click my mouse with the right mouse button to actively cancel it.
I can provide a log if needed.