Pimpernel,
With the best will in the world, that's precisely what happens when you fly off-route in Class G airspace. None of the radar units providing a radar service in that airspace have flight plan information on most of the traffic they are likely to be working. Most of the aircraft either freecall, or are handed over by other similar units. Those units therefore have no real ability to predict when they are likely to get busy. Therefore it is first come, first served. If you are unfortunate to call at a time they are working to capacity, then they answer you received is the most likely outcome. You will note that the units concerned were both civ and mil, so its makes no difference as to who you call - if they're busy, they're busy.
If, however, you flight planned to fly airways (not always easy given the airfield of departure/destination), then you will not be subject to the problems you encountered. The flow through those sectors is based on the mandatory flight planning information provided and 'controlled' by Slots/flow regulation - thus protecting the controllers/sectors through which you will fly.
Please excuse the simplistic explanation, but that's it in a nutshell. If you fly outside CAS, then you go into the melting pot alongside Joe Soap in his C152, Billy Whizz in his Typhoon and any other pilot who wants to freecall to make use of the service/s available. The beauty of the service is that it is there and it gives all aviators flexibility. The downside is that there is only a limited amount of capacity, because units cannot predict traffic levels in advance - s... happens.
Commercial ops in Class 'G' have always been a thorny issue, but I for one (even as an air trafficker) would not want to see the loss of Class 'G' - there is such a thing as over-regulation. But in the end, you pay your money (or not) and takes your chance.
WJMcP