is there any point of moving tempdb files into different disk drive if all LUNs are from the same RAID pool?

There are several potential benefits.

1. Constraining TempDb Growth
2. Making disk-level performance counters more informative.
3. Separating the IO Queues so a log write IO never waits behind TempDB IOs in Windows.
4. Simplifying storage reconfiguration both in Windows and on the SAN.
5. Scaling across SAN controllers and enabling per-lun SAN optimizations.