I never played Rome2, but I have played games that where not only in a worse state than Beta 5.3, but where also less fun even years after release, (Moo3) comes to mind that's still thoroughly broken and no fun. In fact it's disappointment with that that bought me to GC2.
GC3 is already at it's core a great game, unlike Moo3 which sounded good on paper. But Beta 5.3 certainly looks and plays like a Beta not a release candidate, I guess we find out next week if Beta 6 is a Release Candidate or nearly so in our opinions.
For what it's worth I truly hope they are ready to release May 14th and wish them luck, just had to express my doubts.