I'm at work just now so only have a brief chance to reply, but your choice of achievements is interesting. From my recollections of the 'old days', the Continental route was always a far easier route to the World Final than the IntetrContinental.
I've no doubt Muller had far greater resources at his disposal in those days than just about any other rider, especially of course the Poles etc. at that time. While I'm not particularly belittling what he achieved (and that is a good number of World Finals qualified for), I would doubt he would have got anywhere near that had it been a more level qualifying system. Luck of the draw though, those were the times and he didn't have to beat the Brits, Swedes, Danes or Americans. Not a great deal of strong nations left are there?
Continental champion x 4 - not really a big deal is it?. Only have to read the autboigraphies of the likes of Simmons or Morton to realise that Continental/InterContintal/Overseas were all about getting through, nobody was bothered about winning.
National champion - Only won it 5 times?! No idea about the strength in depth of German speedway back then, but it would be a stretch to think there was all that much competition.
Longtrack - I thought we were comparing Speedway achievements, not other disciplines such as long track.