First - I am going to assume that much of what the OP wrote actually happened. However, I am doubtful that Otto M. spent "twenty minutes" calling all and sundry to tell them to be nasty to one specific couple. I have experienced similar behavior on all three of the major European carriers, not on a regular basis, but on an exception basis.

There are some people who naturally are sticklers for the rules - and there are some people who take sadistic pleasure in enforcing rules. I have certainly encountered a few on LH.

One of the challenges of modern airline flying is that when one needs to carry extremely valuable items, there is often very little option. You can check the luggage and risk damage or loss or you cannot bring them with you.

In my own work, I carry equipment which although not nearly as expensive the OP's equipment, is essential to my work. If it is lost in transit, then the entire purpose of the trip is rendered devoid of value, as it is not replaceable except in its country of origin, and then only after some effort. I have had to be very forceful at times to ensure that my equipment comes aboard, even though I do intentionally use a noticeably smaller than European maximum size carry-on, just to avoid any difficulty. I once asked a gate agent to get a tape measure so I could demonstrate that my carry-on was legal. At that point, he acquiesced.

All this said, it is still a rarity in my travels that this happens, and it has happened on every European carrier. American carriers have many problems, but luggage size (at least in business class) doesn't tend to be one of them.

It is rarely wise to abandon a carrier after a single bad incident. If you do, you won't be flying very much. That said, if there is one carrier that I will avoid after many bad incidents, it happens to be the OP's preferred carrrier - US Airways.