A better team of engineers could have designed a safer plug without making it a monstrosity.
Engineers have little to do with it. Regulations drive everything. The regulations in most countries have required that appliances be supplied with a plug for many decades. Some countries are pretty loose about which plug they should have, but they need a plug. For some quirky historic reason the UK is one of very few countries where a plug was not mandated. It costs money, so it was rarely fitted. So, the designers of the plug had to design something primarily for simple hand assembly by the average pleb. Only in the 80s did it start to become a competitive advantage to sell things with a fitted plug. If they had started from the position of designing something primarily for high volume moulded on applications, with a somewhat bulkier option for people needing to hand assemble a plug for one offs, I expect they would have designed something a little sleeker. However, this was not a part of their design mandate. Even a plug designed for moulded on applications would not have been that small. Unfused plugs are a lousy choice when so many appliance cords are not rated for anything like the breaker in the consumer unit. That fuse needs space that most mains plugs around the world dodge, by dodging safety issues. To a large extent we in the UK also dodge this issue, which is sad. How many UK plugs on thin cords for low consumption appliances are actually fitted with a 3A fuse?
A modern moulded on British plug isn't that much different in size from a European or Chinese/Australian 3 pin plug. The greatest meaningful criticism I can see is they never allowed for a compact 2 pin plug which was compatible. On the other hand, most of the places that was an annoyance, like taking a mains powered razor on your travels, have become irrelevant due tot he growth of battery powered products.