Its not a bad passenger aircraft, it just had bad timing.
That’s a distinction without a difference.
The same can be said of all 3 and 4 engine aircraft. For many years, through the 70's and 80' the queen
pretty much owned the ultra long pax flights. Although there were still the 707 which in its later renditions flying routes such as LAX-FRA. there were also some nearly capable 3 holes, but the DC10 got off to a rough start and someone more knowledgeable than me can say why the L-1011 didn't have a greater impact on the ultra long market.
The 747's 1st true competition among the 2 engines was the 777. It was, is and will still be a formidable aircraft for at least the next few decades.
Now there are several aircraft that can match its range and can do so far cheaper. Others have stated why it is still a freighter champ and will continue to be for many years. Maybe not THE best freighter, but will be among them.
The big 3 and 4 engine aircraft all had their time cut short in fairly drastic fashion. With exception to the A380 all the others have served well for decades before becoming converted freighters or just scrapyard material.
Airbus is a smart worthy airline builder and for it to miss the market isn't a show of Airbus making a bad decision or simply rolling the dice with the amount of money invested in it. AND in its first few years there were several airlines who were buying them up as much as they could. It was also about the same time that the 747-8i and 8f was being drawn up and then released. That is how quickly the market changed. The A380 and the 747-8i are wonderful planes. But, just not suited for today's market when there are several twin engine aircraft that can match if not exceed what those two planes can do as far as distance goes. And can do so far cheaper from a fuel economy standpoint as well as a maintenance standpoint.
We still have probably a half dozen years of 747 pax service, decades of freighter, charter and government service. The A380 through attrition hard to tell... again I'll concede my knowledge to others on here, but my guess is about 10 years of A380 service.
Neither the 747 or the 380 were failures. Just victims of rapid changes in the market even the market experts didn't see coming.