Theory is that the thud of valves hitting pistons is transmitted the the bearings and they get damaged.
I'd say that the 16v engine is a bit on the weak side, ok there are a few with big mileage on them but they're the exception. We get offered a 147 or 156 with a knackered engine most weeks in work.
It's all very well blaming poor maintenance and incorrect change intervals on belts and oils but sadly, this is the reality of selling cars to the Great Unwashed. They don't care about such things so you have to build in extra strength to deal with that.
I'd have to dispel that one as the valves are inclined so bend relatively easily. Look at fords 1.8 diesel, belt way too narrow and broke all the time, the valves were direct acting right under the camshaft and they never damaged bearings due to this.
I've also been repairing these engines as long as they have been around and agree with your thoughts that they are not designed very well for general use i.e. missed oil changes, cheap oil, constant abuse (oh look i've just bought an Alfa, listen to this engine at 7000rpm on every gear change) etc.
The thing is, the bearings do not touch the crank (normally) so in theory shouldn't wear, for them to wear they must be coming into contact with the crank (or less often foreign matter) which would point at either the oil, the lubrication system or the design clearances/sizes.
Same with the timing belt failures, this is common with a lot of european manufacturers. They had chains that never broke, then they made belts that did, then they changed from reliable metal tentioners to unreliable plastic ones, then some manufacturers used plastic in their water pumps - which also failed.
Unfortunately plastic is used in pursuit of lightness, manufacturing costs & emissions… yes emissions! You see for a manufacturer to make all these steel components they need a foundry, which creates massive amounts of emissions and due to european pressure they must cut emissions at manufacturing level too.