Ghostblade is internally synergistic, of course, but it's considerably weaker than BFT, adding an item with counter-synergy is not amazing though.
And comparing two items to two items is a whole different kettle of fish, because the number of combinations is very large and thus the conclusions are often inconclusive.
As for the scaling, triforce doesn't really scale, and it's strong. BFT has its own arpen with it, making it superior to most items which deal magic damage, that don't include mrpen.
For the cost, the item gives you everything you can ask for, nearly, and in good amounts for the price asked. I always find ghostblade underwhelming, honestly and get it as part of a "full build" since I already get brutalizer early.