The fight is super easy (even fast) if you READ the announced notes and REACT to them.

In a nutshell:

1: If you kill tentacles, he will reset the arms which allows very little time to dps the head. (don'tkill, just keep away from them)

2. If you kill the arms, he will be stunned for awhile, allowing ample time to dps.

Combine 1 and 2, and you should have no issues doing the fight in a short amount of time.