Of course you could always “play better” this applies to everyone at every level. That being said, bosses like this are heavily reliant on the competency of the group as a whole. Group positioning, movement, smart defensive usage ect can make a 15 feel like a 10 or vice versa. Unfortunately the healer gets the blame from inexperienced players more often then not, so until you find yourself in a group of players who actually know what’s going on this will be your cross to bare.
On a personal level, your expectation is to be able to heal through the web drop movement phase and your group should be cycling defensives during the pulsing aoe screech. If players are dying to rot without stepping on webs you are failing the heal check. If players are not using personals (a health pot is a personal!) during the screech, stepping on webs, running adds into the boss,or not killing the adds before the movement phase starts then there is only so much you can do.
The movement phase is magic damage, and the screech is physical. This is worth noting because of how different DRs work and you can see who’s using what and when. AMS doesn’t work on the screech but works on the movement phase where as physical BOP will immune the screech but do nothing during the movement phase ect.
One last thing- communicate with the group beforehand . “I’ll dome first screech, personals after that” for example. If players are overusing (or not using at all) their defensives, you could potentially fall behind and eventually drown in damage