It's one of the old debates, the extent to which bittering hops contribute flavour. Part of it comes down to personal preference, about 50% of people seem to actively prefer the coarser raspy bittering of something like Target. Personally I don't think something as clean as Magnum is quite right in bitter, it's OK but it just lacks that X factor that takes a beer from OK to amazing. Plenty of small British breweries use it though, and cheap is always appropriate in ordinary bitter....
Scott Janish gives
a good summary of why choice of bittering variety matters - you get sequiterpenes coming out of the hops and also being formed from other compounds during the boil, which contribute spicy/woody notes. Personally I'm not the biggest fan of Fuggles, but you can always tell the beers that use it for bittering. #teamgoldings
Even so, they weren't the first choice in general, it was more a question of brewers getting their hands on any hops they could at the height of the period when Britain brewed beer for the world and domestic hop gardens/yards couldn't keep up with the demand for 150 IBU export beers. It was a fairly short period between demand exploding like that and the invention of pasteurisation and refrigeration dramatically killed the amount of hops needed per barrel, and refrigeration and economic development allowed the colonies to start brewing locally. That import trade had largely died off by WWI, by which time bitter had barely been invented as a named style.
And just because a technique or ingredient was used, it doesn't mean it was considered best practice. Imagine a beer historian in 150 years looking back at this time, they would conclude that since most beer was industrial lager, brewed high-gravity with hop extracts with minimal lagering, that is the "correct" way to brew lager. A British brewer of that time would always regard Goldings as the gold standard for premium beer, even if commercial necessity forced him to use other varieties at times.
