GT6's AI was better no doubt, it would avoid you and acknowledged your existence, but having said that.
That car is painfully slow.
Either not enough power or too much downforce.
You were being overtaken.
Doing 240km/h down the straight even on map 6.
Try the swift sport gr4 with a medium turbo.
With the right tweaks it can do 260km/h on map 6 and its even more fuel efficient.
But maybe you want to drive a slower car for more of a challenge, but a slower car on a track focused on power is not a good thing.