Downside to R2R Ladder DACs?

Since we are an audio manufacturer that builds DHT R2R dacs, this is absolutely false.  That would mean every component would have the same issues since everything has resistors in them.

Dump that sales person.

There is no superiority in r2r dacs, they tend to be more euphonic but sometimes less resolving. YMMV

That all depends on the design of the DAC.

Plenty of electronic components will drift over time.  You probably won't hear it s it is gradual.  In direct comparison if you had a time capsule and kept a new one 20 years later to compare, you may be able to hear the difference.  Not all R2R boards are the same so a general statement is that it won't be a factor.  Is your salesman saying that a chip set won't also degrade or drift over time?  Well at least you will be enjoying your music more until that time comes!

Happy Listening.