I think the turning point for us was getting the first two mobs/phase 1 down more quickly and not allowing a hulk to spawn or, if it did, putting it down just as quickly.
We were nothing like that fast in P1; we'd had one spawn, and would usually get a second at the moment the transition happened - which helped because the timing meant it was easy to completely swap attention to it without anything else to worry about (there's a good few moments before the transition mechanics kick in)
Going into the next phase with full runes was a godsend. Me and my husband tank the fight so once we have to start kiting her around to the runes it because easier when we kinda had a "set" path in mind until the first Reversal of Fortune. After that it's a lot of RNG and split second decision making but I know we can do it now. That's helpful. We didn't expect to get to 5% on that last pull and a misplaced portal kinda killed it for us but now we know and she's gonna get it on Sunday. Last night was a really fun night - I'm glad we extended the raid lock from last week so we could have two nights just to learn her encounter a bit more.
Ah, you're going with kiting her? We did that in Normal, but from discussion with a few other people who'd done some pugging, when we changed to heroic we found that a simpler strategy worked for us, where we keep everything focussed around the central rune; that was a big advantage because it meant we were already well-positioned to deal with the suiciding minions when they attacked. Said strategy
may depend on group size to keep the rune power level under control, though.
I wouldn't change anything if you're now at 5%, but I went from not liking the new strategy at first with really liking how it helped immensely with sensible positioning and swapping targets as required.