The 748 was a product of foresight on the part of Avro who could see a gap in the market when piston types were aging fast, Fokker saw the same opportunity and produced the F27 and both types were pretty successful.
The ATP was conceived as an update of the 748 but BAe tried too hard to make it 'advanced' or as a BAe trainer told me "they took the 748 and designed all the simplicity out of it". The electrical wiring caused many problems and airframe or prop de ice also caused lots of delays. The long noseleg option was supposed to make it possible to operate from airbridges but that was little used in service. It had a not-quite-FADEC engine control systems and a rudder boost system which were also problematic. I had 15 years of trying to maintain them and it was a laugh a minute!