They are designed for those conditions, yes.
However, in the slight past, they were made to as higher quality as they could. (see your 'worthless' A4 which will probably last out most T6.1's)
Nowadays, they are designed to be manufactured as cheaply as possibly with the only 'must' being that they must last past the warranty and after that it doesn't matter.
See wetbelts. I know they are different but this is the mentality that manufacturers have now.
It is pretty much in their interest to have parts that don't last much longer than the warranty period. If an engine goes sizzle, that is great for them. Lots of replacement pipes/bolts/ and the 15k engine.
It would be interesting to know how much of a manufacturer's profit is from new vehicles, finance etc, and how much is from ongoing manufacturing of parts. Given that they can sell all the parts of a vehicle for (at a guess) 3x the price of the whole vehicle. (not talking about caravelle - or equivalent - can't figure out how anything like that could cost 100k)
Unless you are fleet, your business is just pin money to them. Fleets are pretty much just for christmas, and the next christmas, and possibly the one after, but after that, defo not.