Warning disclaimer : There Many answer possible but since we don’t see any videos, it’s only theory how what could have happen. the answer is probably not what happened or maybe the healer was just bad, but at least i may help you get some answer .
Also remember : if you want something done right, you have to do it yourself !
That help to understand the other PoV of with who do you play.
Some healer have mecanics like Holy Paladin when they are close from their target they will heal more with their mastery
Because healer have also the jobs to chain CC to force trinket in front and by so win on the next killing setup with an another control
95% is kinda a lot, do you fake your burst ? Healer push whenyour burst on killing setup and if kill is possible.
Else they got something in mind or you have missed an information
Rdruid hot cost a lot of mana compared to cyclone. By taking cat affinity, you can rake stun a target and chain CC a target and avoiding the dps taking a lot of damage or the dps in front is obliged to play defensively and in both case reduce the damage you take. Player playing cat affinity play a lot based on control. When the healer is control dps tend to burst and when the dps is control the dps “load” his burst so for clone on healer the dps can burn all defensive or kill the oponnent in front.
You can delay demonology burst by making all his pet turning around the pillar while your healer come.
If he hided from you and warlock, that mean the warlock affliction was in total full burst and you tanked spell for nothing.
Many specialisation have spell that do AoE or cleave. if your healer feared to be controled, he can abuse of some spec to make himself free of some control ( example : survival hunter your healer is freezed and with bomb it break the freeze, technically a survival hunter land 100% his trap if well played so the priest have to force the hunter to stop bomb during freezing trap else you gonna die in 1 trap . )
Sometime healer want to tank the interrumpt compared to the caster dps. Example if you have a warlock affliction, the affliction can spam control as long he don’t take interrumpt or control, by so the healer can be saved everytime by his caster and the warlock is freecast doing MASSIVE damage because he don’t take any control.
That’s an issue you didn’t think about but it’s due to the imp AI, if a healer is max range behind a pillar the imp will ignore the order to singe magic your healer and refuse to move. It can be other reason but also not running to your healer can help to your healer to be max ranged.
Shadowland
To understand that you have to see the healer pov in term of mana.
When you add a healer damage , the healer in front is oblige to burn a lot of mana and the tiny control on the healer can force a defensive when no burst happened.
I do that with my mistweaver versus sub rogue/ healer and it result to very often a vanish and since rogue vanished you have a free moment to top back your dps and you with ful hots and start punching the healer for free ( wich is a double L for in front).
Of course you have to be carefull on cooldown etc but at the right time it create mistake for the ennemy team.