Most Mali drivers from the kernel are not contributed by Arm, but you are right that nowadays some contributors from Arm have appeared for the older reverse-engineered GPU drivers, like Panfrost and Panthor, and now there are also a few GPU-related drivers, like HDLCD and MALI-DP, which have indeed been contributed by Arm.

Besides the Mali generations that are supported in the mainline kernel, there are many other Mali generations for which Arm has not provided anything else except closed-source drivers for Android, in a few cases also closed-source drivers for Linux. However, there are many other reverse-engineered Mali drivers, besides those from the mainline kernel.

It is good that Arm has begun to contribute to the kernel DRM drivers, but these drivers do little else except providing the means to communicate with the GPUs. The complex work is done in the user-space GPU drivers from Mesa.

The Mesa Lima driver, for older generations of Mali, does not have any contribution from Arm.

In the past, Mesa Panfrost was also completely reverse-engineered. Seeing that now Arm has begun to contribute to the kernel Panfrost DRM, I do not know whether they have started to contribute also to the Mesa Panfrost.

In any case, while some contributions to the previously reverse-engineered drivers are much better than nothing, what would have been much better is to publish the technical documentation of the Mali GPUs, in which case it would not have mattered whether Arm contributes something or not, as anyone could have written the drivers.