I would suggest, Peter was a very competent driver, especially long distance, but, not deserving (maybe) of the hero worship he attracts
Perhaps he was born ten years too late? By the time he got into his stride, Australian racing was really a bit 'provincial' and there didn't seem to be that steady stream of Antipodeans coming to Europe that we saw in the 60s. I guess Bruce's death and Black Jack's retirement had a lot to do with that - there was no longer a guaranteed 'home from home'. The end of the Tasman series must have been another factor.
Speaking as a Pom, I reckon Brock could probably have cut it in Europe in touring cars and maybe even in endurance racing, but I wouldn't put him up with the greats of endurance at the time - he was no Bell, Ickx or Wollek and I'm not sure he would even have aspired to that. He chose to (mostly) stay at home and be a big fish in a small pond and maybe you only have to look at the experiences of a few of his contemporaries who tried and failed in Europe to get an idea of why: Perkins, Walker, Schenken ...
Added to that, Brock didn't have the open-wheel experience which was then pretty much the accepted way to get to the top in Europe. You did FF/FV/FFrance, F3, F2 and then hopefully F1: some, like Elford, took a different route, but getting an F1 seat was the way to get yourself noticed - even by the sports car teams. That was the way Vern Schuppan did it, for one.