The teach with over 20 years experience in the cable buisess said that anytime you install a non-conductive substance between a metal to metal connection, the connection will be weakened.....It does makes sense to me.
We switched to "F-Seal"...Multilink made it. On the tube, it said that the connection was made at the mandril, not at the threads; therefore the connection was not affected.. It was more of a teflon type, than silicone grease based. Using the teflon based compound also provided a better threadlock; it was less likely to allow the connector eventually vibrate off.
As far as not using connectors with o-rings....unless the port is 100% smooth and the mandril of the connector has not been bent at all...you are right, you do not need the o-ring.
I worked for one of the cheapest cable companies, but they still used the connectors with the o-rings, even back in 1989 when the SNS was new, because they decreased the number of service calls due to corroded connectors.
I can see where young techs could say that weather boots are a must. I recently had a COX tech tell me that, but I have pulled away several weather boots and saw lots of white corrosion.
The best way I ever saw was that company which used teflon on the threads only, not inside the connector near the mandril. The teflon prevented wather travelling down the thread inside the connector. The O-ring inside the connector prevented moisure coming in from behind the mandril. The Compression from the snap-n-seal connector prevented moisture from getting inside the cable. There was a metal to metal connection at the mandril.