signal leads that pick up less ambient noise?

The whole point about coaxial connectors is that the distributed capacitance and inductance gives you a R50R transmission line. The only way to get "ringing" out of that is to fail to terminate the transmission line with it's characteristic impedance. In practice it is hard to do it perfectly and you do tend to get low level reflections, but they die out fast,

The message is rather more complicated than that. The later editions of Ralph Morrison's book do go into that in more detail than the earlier editions.

The sixth edition only mentions the "feed-through" capacitor in one paragraph on page 65. The fifth edition does not mention them at all as far as I can tell.

Feed-through capacitors seem only to be used in RF electronics, and Ralph Morrison's book initially concentrated on regular industrial electronics. Later editions did move on to higher frequency applications.

I never used a feed-though capacitor anywhere in the work I did - if we need to put a fast signal through a conducting bulk-head we used coax feed-throughs. Feedthrough capacitors are relatively exotic devices.

Your example of their application seems to be a case where an RF specialist went in for a bit of over-kill.

Industrial electronics may not contain RF devices but they are more and more likely to be exposed to strong RF fields from external sources such as mobile 'phones. Putting critical circuits inside metal boxes with filters on the incoming wires is much more prevalent now than it was a few years ago - the circuits haven't changed but the hostile environment has.

Relays and cam timers may be set to make a comeback.

I recall back in the days of crt based displays when my phone was sat on the desk near it the picture would break up a couple of seconds before my mobile phone rang for an incoming call.

So how is it that when I Google feedthrough capacitor use I get this:

"Feedthrough capacitors are used to filter out electromagnetic interference (EMI) and radio frequency interference (RFI) in electronic devices. They are used in a wide range of applications, including medical equipment, power supplies, and communication systems."

Ok that was generated by AI, and it's true that in the last few days I've had at least one blatantly wrong response. So I tend to ignore the AI generated responses but in this case I'd say it's reasonable.

The OP does not need coax feed throughs. Simply using a ground plane may be sufficient,

I don't see anything exotic about a capacitor to ground at a metal enclosure boundary. I can imagine a road sign at the boundary. Noise and RF follow ground. Low frequency signals keep straight ahead.

If the OP needs filtering at all then a capacitor to ground at the enclosure boundary is likely more than sufficient. Going to the trouble of putting it at the enclosure boundary is also possibly not necessary in this case. Put RC filtering on the board as needed. Feedthrough capacitors are becoming more expensive due to not being used as extensively as they were in the past.

Actually this is just a case of you making yet another completely wrong assumption.

In the OP's case filtered connectors may be overkill and too expensive but it is worth knowing about them.

Anyone designing medical devices these days should be sure to take account of the effect of a mobile phone an inch away. After all it's no longer possible to keep mobile phones out of hospitals or out of anywhere at all unless you want to search everyone on entry.

I'm sure you like to think so.

One thing to notice that RG58/BNC cables are not created equal. There is big differences in transfer impedance (shield effectiveness). Some Chines cables are good, others are crap.

A good coax cable is quite expensive.

When doings measurements on either conducted immunity or using near field probes, it get even more evident that the cable quality has a large effect.