Tired of This Sh*t SE (SCH, Keep the nerfs don't care) But..

[Koltik]

It's not about being focused itself. When a PLD/MNK/whatever gets focused they can continue to perform the role they're there for- DPS'ing, just with an aspect involving defense.

No, we are being attacked and thus are being stunned, heavy'd, knocked back, rooted, and god knows what else. Any one of these make us lose footing on our target, and we are no longer functional. We still get some hits in, but we aren't going to be performing near our full potential.

A Healer who's role is to keep the party alive, not just themselves, was already limited in being able to perform their essential role to the party when focused and had to shift to survival mode, severely limiting their ability to heal the party.

See above. Melee DPS also become very limited in performing our role when being focused. Caster DPS are on the same boat.

Do you think a SCH being CQC'd by multiple opponents should be practically OSK'd and die in seconds, with the remaining party members having a major reduction in healing of up to 100% if no healers are left

If you are all by yourself healing then yes, you should die. Your group needs more healers. PvP was balanced around WD; in WD you have 2 dps, 1 tank, 1 healer. If you disrupt this ratio then of course you will have issues.