The problem with the Marinide Sultanate was mostly "internal". Problems with their viziers and distant relatives (Wattasid) who would end up ruling Morocco as regents of child sultans (who are assassinated at their coming of age for a new Wattasid regency), and later replace the Marinides as Sultans.
Examples of little internal stability are the Azemour Rebellion, the partial autonomy / independence of the Tribes in the Tafilalet region (where the Saadis originate) and the independence of Marrakech by the Hintata, Confederation of Berber Tribes.
Furthermore, the lesser princes of the Marinide dynasty were also troublesome, the Hintata used a Marinide Prince as puppet Sultan of Marrakech to declare independence (later the Hintata would choose a Hintata Sultan). The Emir of Granada also freed Marinide princes (prisoners in Granada) to place them as Sultans of Morocco (technically Sultans of Fez, the name of Morocco did not exist)
In short, if the Marinides of Morocco make an effort to consolidate their power (especially in Marrakech, Marrakesh is like the second capital of Morocco at that time, it is very important geographically and militarily), they do not spend resources in helping Granada (they are treacherous) , they eliminate the Wattasid (there was a plot where almost all the Wattasid died, they all have to die), and they eliminate the distant Marinide princes (they are very troublesome), they should have a tight grip on Morocco.
PS: the Marinide Sultanate / Sultanate of Fez (Morocco) should partially conquer the Zayinide Sultanate / Sultanate of Tlemcen (Algeria), little by little. Algeria has almost the same population, it is impossible to "integrate" the entire population of a single conquest. For me, the main problem in Morocco is overextension (conquering Algeria and Tunisia only to lose them in two decades), it does not make sense to spend resources on territory that they could not maintain (a lot of territory)
PS2: Eliminating the Wattasid would also be useful to add their lands to the royal domain of the Sultan. The Wattasid ruled a large territory northeast of Fez (roughly where Debdou is if I'm not mistaken). If Morocco were a Catholic kingdom, the Wattasids would be powerful dukes who deposed and replaced their monarch.
PS3: A Marrakech firmly under Marinide rule destroys any Portuguese ambition on the shores. The Saadis demonstrated it.
PS4: It also seems to have been common for the Marinide Sultanate / Sultanate of Fez to be divided into a Sultanate of Fez (with capital in Fez) and a Sultanate of Marrakech. With the parents giving inheritance to another son. Obviously this caused dynastic problems between relatives. The Sultanate should be "indivisible" and avoid problems.
I don't know much more about the region. I hope I have helped.