I consider them both close to the last words in hifi.
Let me elaborate a bit so there's no misunderstanding. When discussing truly hifi loudspeakers, "Heresy" and "LaScala" are two of the last words i'd ever use. In my world of hifi they are at the entry level. There are just too many better loudspeakers out there.
They're high sensitivity loudspeakers, i'll certainly give them that.
But, high sensitivity is expensive and many high sensitivity loudspeakers pay dearly for it in multiple ways. Rolled off response at both ends is usually the highest price, Heresy and LaScala could be poster children for this. Low end extension can be purchased back with increasing box size. You gotta go real big to maintain sensitivity and extension. No matter how you fold it, a horn has to be big to go low.
IMO, the Cornwall is hands down the best balanced of the bunch, the K-horn could qualify but the proper set up is only possible in certain rooms. I lived with Cornwalls in the mid 70's and once thought they were the greatest speakers ever made. Once i heard and lived with multiple better loudspeakers, my perspective changed greatly.
I cannot take that away from them, i have heard Heresies rock the house all night long on big power too. But, in all fairness titties and beer were also equal parts of that equation.