MSTP and RSTP

Good morning,

I have a question that I haven't been able to find a solid answer to, the general answer I get is it's backward compatible so it doesn't matter. But I wanted to ask the hive mind of r/networking for some possible clarification.

The scenario is, a Juniper stack is running RSTP as the root bridge. I have 4 HP Aruba 2540's running MSTP, since that's the default when enabling spanning-tree on the Aruba switches. I know that MSTP and RSTP are compatible, but I think a majority of these scenario's probably look more like MSTP on the root bridge, RSTP enabled on the switches. My scenario is vice versa, and I know MSTP groups by VLAN. My question is, is there still a benefit of MSTP when the root bridge is RSTP? I am still new to STP in the real-world and only know of them conceptually as individual pieces. I haven't worked with them between vendors and different types of spanning-tree before.

I inherited the network and am not sure why the Juniper stack would be running RSTP and not MSTP as the Aruba's are. But, the same people that set this up also didn't see it as necessary to have spanning-tree enabled on 2 out of 4 of those switches which caused me a headache last Friday as a broadcast storm took down our network.