In being completely ineffective in every situation, and thus having no true purpose or situation for its use, Physick is useless; in having a noticeable effect in a niche situation, or having a particular use, any of those other abilities have times where they are very useful.
I honestly don't know what you're talking about. There are plenty of SB duties that have foes which are affected by sleep, heavy, bind, silence, pacify, stun, etc. If "SB duties" was supposed to mean "SB raiding and trials" then, yes, unless a duty has a specific mechanic involving them you have a point. I'll admit the emphasis on speed and DPS output in duty finder parties means that crowd control is often ignored but it is still effective if a group wants to use it. If we're being fair about whether something is useful or useless in FFXIV you can't carve out whole categories of content.
My point in calling a Summoner's Physick useless is that it is ineffective in every situation, in nearly all content (Arcanist/Summoner Physick is crappy-but-functional until Caster gear loses Mind at iLv50), in the game -- definitively ineffective in all of HW and SB. It has no specified use.(not solo like msq, potd, eureka etc)
If we are "to correctly define" useless then its first definition is "not fulfilling or not expected to achieve the intended purpose or desired outcome." Nearly every other ability achieves its intended purpose in one type of content or another. Summoner's Physick achieves no purpose nor outcome regardless of the type of content; starting from iLv50 and continuing through HW and SB it is never worth it.To correctly define "useless" is something that does absolutely nothing in certain situations. Target immune to Sleep well Ripose is no good, immune to Bind that's Tether out of the window. Physick still does something even if it is pitiful and barely worth it.
Physick for Summoners is entirely ineffective. Fix Physick.