Thanks to trade treaties, ESA always has to use the cheapest available hardware that fulfils the requirements – no matter if other hardware is more reliable.
This has been part of many discussions before – and it doesn’t just affect ESA.
From government agencies which have to buy pencils that break after every use and are practically useless, to contractors building Autobahnen where the asphalt melts in the summer sun away.
You're bringing up a non issue. Add reliability constraints into your requirements. Airplane components are also made of the cheapest materials that satisfy the constraints required by the engineers and they don't randomly fall apart.
Perhaps you should use actual statistics for launch and slingshot failures, because those numbers are actually available. Also consider that the design of an RTG probably takes those risks into account.
Talking about it like it's incredibly obvious isn't really productive.