The Denon DL103 is an example. It can be improved by a different cantilever and stylus. JICO made a living by producing improved stylus / cantilever packages for cartridges. That doesn't make the designers stupid. They just designed to a price point.
@bpoletti The idea to produce styli for discontinued MM cartridges is great, but JICO also made them to keep the price low, except for SAS which is the most expensive. But even SAS can't surpass original MR on many vintage MM, i think they are equal. Cheaper JICO styli are not better than originals (especially those originals with beryllium cantilevers), it is only compromise (something better than nothing) for many owners of old MM.
Upgrading a Denon 103 does not make its designer stupid, it was designed in the 60's and today standard is different, but it's questionable (at least for me) why not just buy a better cartridge instead? If someone willing to end up with triple price with their DL103 it's ok, but i just don't get the logic behind this process since better cartridges available at the same price.
Regarding modern cartridges i think it's possible to buy a better one, no ?