I think that zukahn1 hit the nail on the head in that the over-pricing of these parts today leads to performance expectations not to be met!

Yet, when evaluating old parts, it seems fair to use contemporary replacement bits like chain, pads and cables for a more-objective evaluation.

Starting with the brakes, yes they seem flexy, and have the cable on the wrong side of the calipers, like so many DiaCompe and Weinmann calipers also do. With modern cabling and well-chosen modern pads that dn't require a lot of toe-in, these brakes are passable imo.

The crankset is light and looks nice, but is on the flexy side as one might predict by looking at the dimensions.
The chainrings have the useful, patented W-CUT features of pairs of shortened teeth for faster, more-assertive shifting action.
The 6mm self-extractors caused real problems though, both with installation and removal. One should always apply weighting to the pedals, then turn the cranks 180-degrees and weight them again repeatedly during both the tightening process and the loosening process, between "rounds" of bolt tightening or loosening. This will settle the tapers fully using a lower torque value, and will also extract the arms without stripping the hex or possibly pulling out the extractor threads. All this adds to the assembly and servicing labor.

The hubs were excellent, but the freehub versions were faulty. Many of the hubs (also the "Model 60" version that so often was paired with the 600 parts) developed a failure of the attachment of the inner freehub body to the snout on the hubshell, which did not affect the performance but which made the cone adjustment process maddening, since there was added rocking freeplay to factor into the equation. Dura-Ace model freehubs from this period threaded the steel inner freehub body directly into the hubshell, avoiding this problem.

The front derailer was pretty normal. The rear derailer had a near-identical actuation ratio to Suntour and to even the later Dura-Ace SIS rear derailers. The "B-Tension" positioning was pre-set so as to handle at least a 28t cog, so the chain gap was large when used with smaller freewheels. One can disassemble either of the body pivots, A or B, and drill a new hole for the end of the spring. Depending on which spring, and depending on the position of the new hole, the body angle can be finely adjusted. Simplex also used dual-sprung derailers which conveniently added a locknut to the cage pivot attachment, so external adjustment was possible with their version!
I have more than once noted a big improvement in shifting when the Arabesque rear derailer was replaced with a 1st-version 600 SIS unit. The later model featured the first-time use of a lower actuation ratio for Shimano, so the lever movement increases noticeably and shifting feels more forgiving. The newer 600 derailer also had a variety of other detail improvements that even the "New 600EX" derailer did not have.

I was nearly sickened by the looks of these parts when Shimano rolled them out, but nowadays I see them as they are and, like another poster, I tend to collect the cranksets (the majority of which featured a one-piece crankarm/spider, ...some were two-piece btw).