Hi Pekka,
I apologize! I must have answered this from 'memory' and did not remember it correctly.
You are right, there is no way to 'disable' the link to open the PPM Gantt from within Classic or from Clarity NUX (the new user experience).
If you don't have that 'scheduler' access right, it prevents you from doing any 'tentative' or 'autoschedule' changes, but does NOT control the access to the Gantt.
Having the ability to turn it off is a good idea. Please get it logged, and if other customers like this idea and it gets voted up, we can do something to control it.
Once again, I'm sorry that I provided incorrect information to you.