Alright sports fans, over the past month I've watched every single one of Dariusz' fights on Youtube. Literally, every single one. I doubt any of you can say the same thing. Here's my take on him.
Definitely Top 10 LHW on the all-time list. Without question. He fought top quality opposition throughout his career and had a habit of beating them definitively. Rocchigianni, Thadzi, Hall, Hill, Griffin, Piper, and Barber were all top ranked LHW's when he fought them and he clearly beat all of them. Go look at all-timers like Bob Foster and Dick Tiger's records; their records are padded with far lesser fighters interspersed with big names. Just because he never left Europe to fight does not automatically mean his opponents sucked.
To watch him evolve as a fighter was really amazing. He started out as a basic pressure fighter with a huge right hand and left hook, with a decent front headlock (watch his fights) and not a whole lot else. As he grew, he developed the P4P most devastating jab I have ever seen in boxing. It wasn't the fastest or even the best but it was literally the most powerful jab I've ever seen from someone at 175. That thing damaged fighters' souls and was the major reason for a lot of his stoppages that occurred past the 8th round. His cardio was ridiculous too. No one was able to handle his pressure for 12 rounds without looking like they were going to explode and he always finished fights looking far fresher than his opposite man. His chin and overall toughness were absolutely amazing too, that first Rocchigianni fight notwithstanding. Gotta admire his ability to cut off the ring as well. Overall, he was one of the best pressure fighters LHW's ever had.
That being said, RJJ would've beat him pretty soundly, like he did to everyone else at LHW. DM didn't have anywhere near the head movement or foot speed to catch up to Roy or defend the barrages that would come his way. Again, no shame in that, seeing as no one else did either till Roy came back from HW and hit 36. If we're going to be honest with ourselves here though, RJJ is the 168 and 175 pound GOAT and in his prime no one should really be considered a favourite against him. IMO.
To conclude; in answer to your question TS, Der Tiger was freakin' awesome. One of the most entertaining and successful fighters of his era (despite the fact that most North Americans don't know much of anything about him) and one of the best LHW's of all time. Just not THE best.