"Removing the Elephant diffuser doesn’t entirely break BitLocker. If someone steals your laptop, they still won’t be able to unlock your disk and access your files. But they might be able to modify your encrypted disk and give it back to you in order to hack you the next time you boot up"
That is true of practically every full disk encryption package, because of the nature of encrypting disk sectors rather than files: with no format flexibility or straightforward place to store metadata, and no awareness of message boundaries, it is difficult to meaningfully authenticate data.
Vanilla CBC makes it easier to mount attacks, and XTS makes it harder, and the diffuser may have even made it incrementally harder. But no notion of difficulty here deserves the uppercased "Hard" we're looking for with cryptography: at best, you concede attackers "only" the ability to randomize targeted ranges of stored bytes, which --- especially for the mountains of C code we call "operating systems" --- is a devastating vulnerability.
If you are seriously worried about Highly Capable Attackers, and you lose custody of your laptop, you should consider writing it off.
I think it's best summarized as:
"Removing the Elephant diffuser doesn’t entirely break BitLocker. If someone steals your laptop, they still won’t be able to unlock your disk and access your files. But they might be able to modify your encrypted disk and give it back to you in order to hack you the next time you boot up"