No kidding. Soylent 1.0 had 60 mg of sucralose per bag; 1.6 had 23 mg per bag. That's pretty significantly lower per calorie. It's definitely not the sucralose or I would have hated many other products, including Food Bar (about 30 mg per bar), which I loved.
I've also got a bag of sucralose powder in my kitchen. One of the first things I did with 1.6 was try adding some, which made it taste sweeter but did nothing to mask the taste. I also tried cocoa powder (with and without additional sucralose) to no avail, and after all that failed I tried purchasing a bunch of flavor oils (mentioned in a thread here); none of which were able to effectively mask 1.6's flavor.
I know you think you're right, but you've done nothing to convince me. I'm open to suggestions. Seriously. Even though it doesn't matter since 1.6 is no more, and I don't think we'll see a regression in flavor from 1.7... but I'm still curious if anyone has any plausible theories.