Isn't that normal (a lack of acceleration in top gear)?
Normal in the sense that you get the lowest acceleration in 7th gear. But not normal as in you can reach a higher speed in 6th gear than in 7th on this track. Especially since you get into the red zone in the 6th gear a little bit past half of the start/finish straight.
p.s. Managed to improve down to 1,19.608. Staying in 6th on the straight definitely helps - I think it gives you around 0.1s judging by my first sector time.