I play both steel string guitars and nylon (classical and flamenco).
Based on some of your initial questions I think the main issue here is that your experience is all steel-string and you haven't had time to adjust to the nylon string instrument. They really are very different in many ways.
Sustain is a big one, you are not going to get the sustain you are used to out of a nylon. I play a lot of flamenco as well so my guitars sustain even less than good classical instruments.
Intonation. I have found a similar thing with less expensive (sub $1000) instruments. The intonation higher up the neck can a bit off.
Dull strings. Unlike steel strings which often dull in a few weeks and all strings are affected, nylon strings definitely are different. The trebles (G, B, e) usually have longer life and don't need replacing as often. The basses (E, A, D) need replacing more often. That is why they sell nylon strings as trebles and bass sets to facilitate this. Also, on many classical guitars, the nylon G can be notorious for being more dull (tubby) than the B and e nylon strings. In general the only real solution I have found for this is a high quality instrument. You can get wound G strings to solve this but they seem to introduce new issues (break easy, etc...).
Also, just a heads up, new strings can take WEEKS to settle in, especially the trebles. They just keep stretching and stretching.
I love playing both types of guitars but approach and expectations have to be different for each. If you know someone who is an experienced classical player having them try instruments with you is a good way to go. Of the brands you mentioned my preference is Cordoba. I would also say try a flamenco guitar too, while usually less sustain, they are brighter with more attack. I play lots of classical music on my flamenco instruments and they sound great. Only the "cork-sniffing" purists would fault you for that
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Later
Rob