Okay let me clarify this: This is only the case if you're running long length's or running the RCA cable together with other wires/other equipment that create noise. If this is both not the case, then you probably don't have an difference indeed. So "extremely degraded by an rca connection" is indeed not always the case.
But since most cables just "run somewhere" together with audio equipment/computer equipment/power cables etc.etc. an balanced connection is always better and a degradation in signal is practically always the case with unbalanced, simply because unbalanced is unshielded(the shield is part of the signal). Maybe audiable, maybe not, true, but it's not optimal and it should be avoided.
Maybe you never had GND hum issues with unbalanced connectors, but many others had. So there is not a single reason not to include XLR, it's simply an better connection, all these issues are avoided by simply chosing for balanced connections. The big Arendal's and most other big/huge subwoofers have XLR's, only the small sub's don't have XLR which is a shame, this is a shame since not everyone has a huge living room but some still love to have good equipment while also having a living small.