For years I've used 30lb Amnesia in black or clear or 40lb Drennan Grey Greased Weasel.
The clear Amnesia is not as supple as the dyed versions.
Like @yonny I'm a dinosaur, if it works stick with it, although I have tried using tapered leaders, for carp and sea fishing and for some reason I kept on cracking off, so went back to the straight leaders. I would say that it might have been my knots, but my mate Allan tied a few up for me, but I had the same issue, while he had no problems with long casting.
The other advantage is that I can go longer than the 4 turns on the reel and casting drop, I normally have around 5 or 6.
I also use them on my Spod/marker rod to braid.
Point to note, as I have mentioned to Yonny in the past, if there are snags or weed I won't use a leader as I don't like the risk of leaving a leader that the lead and rig can't be ejected if you crack-off.
With weed caught around the knot even a run ring can't come off over it.
Again like Yonny I've gone finer than 12lb; for years we used 8lb line (Sylcast or Maxima) with leaders on 2¼ or 2¾lb test curve rods.
It's probably only since the 1990's that lines rated 15lb or more got used for carp fishing.