For every Tide, there is a Gain.
SOPUS positions Quaker State products at a lower price tier than their flagship Pennzoil brand. Formula Shell is on a little lower price tier and its distribution tends to be limited to pay to play warehouse type retailers, although Menards stocks it around here.
If you compare quantifiable things like add packs and cold performance, QSUD is the equal of any other OTS 5W-30.
It's priced at a lower level for those who don't quite feel like popping for an extra three or four dollars for M1 or PP.
The price tier at which QSUD is offered is more a matter of marketing than it is of product quality. SOPUS wold prefer to keep the value buyers in the house, rather than have them turn to ST or MSS.
The guy who pays a few bucks more for M1 or PP feels like he's also getting a few bucks more in quality while the guy who grabs that jug of QSUD feels like he's gotten a deal on a full syn labeled oil for a few bucks less.
Either way, the buyer is getting a quality oil.