You are absolutely right - I'm sorry. So yes, maybe they should have rerecorded. Perhaps they thought the main draw would be Patti, and for that reason alone felt they didn't really need two recordings. (Whereas, for instance, Spider Woman got rerecorded when the cast changed over, but all 3 leads were different, and I suppose they felt differently then. It was also a different time then, and cast recordings are more of an expense than they used to be.)
And yes, much as I adored Lenk in The Band's Visit, from all I've heard her Bobbie wasn't nearly as good.
I wonder if they felt the stiff upper lip Brits just wouldn't appreciate "Jesus Christ" used in that context. ;-)
BTW - it's also interesting that Larry Kert had to wait for London to get recorded in the original production, even though he took over for Dean Jones on Broadway a month after the show opened. And for that recording, they just replaced Jones' tracks with dubs by Kert.