On the contrary, plastic has many advantages.
Doesn't rust, doesn't condense, flexible, less joins required, vastly shorter fitting time so lower labour cost, lower parts cost, similar lifespan, easier servicing to name but a few. I wouldn't call that a bodge at all.
Water can be dosed with whatever you like.
Copper is not chewed by rodents!
Copper withstands at least 250 C ( which melts the joint solder ).
Copper does not sag.
Copper can be removed and reused elsewhere.
Copper has a scrap value which can be reclaimed at any time in the future.
Plastic has it's limitations and has strict guidelines where it shouldn't be used (gas, oil, compressed air, steam) and is ok up to a short malfunction temperature of 118 deg c at 3 bar. Seeing some boilers are set at 82 deg c max (condensing boilers less) temperature shouldn't be an issue.
Thanks,Always PB more flexible and easier to work with.