No. Lookahead reduces pauses, which increases overall TPS. Yes, you turn slower, so your peak TPS is lower, but overall TPS is higher. Proof: your time still equals movecount / TPS, and since lookahead doesn't change movecount (except when you're advanced enough to be able to look ahead into multiple pairs and choose the most optimal one, which definitely is not the case for a 12 second solver), only TPS, and TPS is in the denominator, time is inversely proportional to TPS. Since we know from experience that lookahead reduces time, it must increase TPS.
However, this is a bit off topic so if you want to discuss further just PM me