QSS being good on those 2 champions is more a result of them doing well to begin with and any reasonable purchase helping them out.
With a 90 second CD it's hardly the CC trump-card you're making it out to be. That's ult-level CD times, not so much QWE CC.
Also: QSS is a bit of a sacrifice in core-build power for pretty much anyone, and is more something you'd get if it can make a really big impact.
It's important to note with item costs a typical game is only going to give 11,000 gold per player - which is 3 major 3k items, 1k for boots, and 1k in the bank when someone's Nexus explodes. Or 1 major 3k item for early, mid, and late game.
While QSS is certainly cheap enough to add into a build when warranted, even a 1250 item can really set you back.
Finally: it's worth noting most CC heavy/CC is their shtick champions apply CC in such a way QSS is useless vs. it.
QSS cannot do anything vs. pulls, flings, knockbacks, or knock-ups. QSS also cannot remove terrain-based CC like Glacial Storm, Mega-Adhesive, Gravity Field, Iceborne Gauntlet, or a myriad of other slowing fields. And QSS can't do anything vs. sudo-CC tera-forming effects like the walls of Anivia, Azir, J4, or Trundle.
Vs. an Alistar it's 100% useless, vs. J4 it's 100% useless, vs. a Blitzcrank all you can remove is a 0.5 second silence.
Not sure I'd call QSS a tad bit broken.