Quick question about Tanking in Ifrit HM

[Huntington]

I'm usually the Off-Tank since most others I see have more HP than me, only got PLD to 50 two days ago and the gear I had stocked up was meager at best. Yesterday in a run, I stunned whatever I could, when I saw an Eruption go near a healer, I'd stun for it. If I saw the Plume attacks pop up and thought someone could get hit by it, I'd go for a stun. If I could no longer stun because of Immunity, I'd inform the party to be on their toes.

As the fight went on, a DRG stunned once or twice himself and messed up the rhythm, people started getting hit by the Eruptions later on, and we had a few people go down, myself at one point as well. Once Ifrit was near 3/4ths HP, others were struggling to dodge the plumes and Eruptions, by this point leaving the stuns to me was not favored even though I'd been doing them perfectly timed up until the snags started when I could not stun because of immunity.

At the end I was told I was an awful OT and should stop being a scrub and play better. Just yesterday people complimented me on doing the stuns and I had several runs before that where no one complained.

Was this an actual error on my part?
(Hit posting limit, will check on this again later)