I'm not sure what the argument of a Prius not being a fun car to drive (or, as you said, purely a too, to go from A to B). I agree nobody would ever buy one for the enjoyablility of the handling or "performance". It's 100% about economy.
But, I also wouldn't classify a TDI as an enjoyable car to drive either. I've owned them for 4 years now and can't say I've ever really thought about it as anything more than an A to B either. It has more functionality than an older Prius, but the newer Prius "wagon" has a decent amount of space.
I feel that both are primarily purchased for fuel economy. Both do that well. Personally, when I'm looking for a new , economic car to replace my TDI, I don't think I'm likely to buy another VW.
I've driven literally 1000's of cars over the years, owned too many to count, and most of the cars are as said, boring to drive, don't handle and don't have any power, or you give up options. Newer Honda's are great but the price tag, ouch and I was driving a 2002 Civic for awhile, not bad but no smile on my face, it was vanilla, lol. I love jumping in my 2000 and driving, its roomy, comfy and fun to drive. Going up stupid steep hills at 130-140 km/h with ease sure doesn't hurt.
I went camping this summer, 2 adults, 2 kids and all the gear in my sedan, not sure I could have done that with other car's I used to own. Also, I up until I bought my TDI, I was not a VW fan, not sure why, just never got into them, now I am kicking myself,
Most cars start to fall apart after 200K, both my sedans have 400k and 377k, my TDI wagon has 220K miles and drive like new cars, even my brother in law who I sold the green sedan to, 400K, can't believe how quiet it is, how the doors thunk when closed. He currently has a Cavalier and a new Tundra, he is selling both and buying another diesel VW, probably a Wagon.