I wouldn't think "produplicated" is much better than just burning copies.
I guess it is one part about burning. Other part about medium.
I would guess, the simplest mistake is to buy cheapest possible CDR media, and as result you got crap. Price difference of cheapest discs out there, and those which are considered to be "for professional use", is quite small. I don't see any point in thinking about saving money whether bulk disc costs 0,20 or 0,50 or such. For better brands, I would guess many people suggests "Taiyo Yuden" to be along highest quality discs. If you got burner that works, computer that works, then I see no reason why data would be somehow less quality on disc than when it comes from some company high-speed burning towers. One can buy such machine for himself too. With functions like proof-checking discs for mistakes etc.
In additional question you ask CD vs cassette. Not sure do you mean pressed cd or CDR. But if we compare CDR vs tape, I'd say that current situation seems to be that:
-CDR interests almost nobody
-Tape interests much wider group, as does pressed CD.
For me, CD is still easily the best selling format, that goes far more than vinyl and tapes. But under very specific conditions. It's most of all case of audience. People into small bands and certain types of stuff, seem to go for tapes and vinyl. The bigger the band, the wider audience still goes for CD. Often in case of tapes, you move them quick - but limit of maximum units you can move is reached fast. CD may start slow, but keeps moving for longer time. This has also a lot to do with.. lets say "economics of noise" what may have been talked in some topic before. CD is perhaps only format what theoretically has more potential to be taken by distributors. Cheapest shipping, often easiest to storage.
If someone asks my opinion, I'd say that forget CDR as medium of publishing. It's good format for sending promos, giving out stuff to allies you are in contact with. But if not willing to go all the way for "proper release", might be better to open bandcamp or soundcloud.