My thought on s8 earphones. Note that I also own another RM400+ AKG earphones so some expectation will be there since some claim it cost 99$ price value similar price range.
My honest opinions (please don't shoot me XD)
Sound clarity: 7/10, some how the volume is slightly lower compare other individual sold earphones, but has OK sound clarity.
Sound bass: 4/10, bass is definitely lacking for bass lovers.
Noise isolation: 7/10, okay.
Comfortable: 8/10, can immediately notice this earphone is quite comfortable to wear with its design.
Build design & quality: 7/10, plus point on tangle free design wire up to split section but have to minus marks due to rest of wire using rubber and confirm wear and tear won't last long same with my another AKG earphones.
Summary: Considering it is a earphones supplied together with phone the overall sound quality is noticeable better. Would say this is good earphones beside the sound bass and overall volume is really lacking for my personal taste.
I agree with your assesment, my cheap JBL earphone sounds better than the bundled one.. quite disappointing really, considering the hype. But I guess it depends on individual's ears.