I think that the question depends upon what you want out of PvP. Put briefly:
* if you want an enivironment where the individual's skill is paramount, then you need to have every profession be relatively flat in terms of strength - that is, they should all have about the same level of strength in all areas of offence and defence. This has to be balanced for one-on-one play in a group environment, where you can't choose your opponents.
* If you want professions that have individuality and uniqueness, then they need to have both strengths and weaknesses. Here, a more rock/paper/scissors approach is needed for one-on-one balancing... which has its weaknesses. But in teams, this system has great strength because the professions are designed such that they fill in other professions' weaknesses - while other professions fill in theirs.
* If you want an environment where (at least in theory) tactics and strategy, like in war, are applied, then you first have to create the environment where that works before profession balance becomes an issue at all - and AO doesn't have that environment at all. Where it exists though, you perhaps have the strongest need for specialism in professions without the holes in their abilities needing to be filled in by others. The tactics on the grand scale is what balances them out.
As a result, a lot depends upon player motivation. I'd say that most PvPers in AO that are regularly active and certainly the ones that tend to be vocal in the forums, fall into the category of wanting individual player skill to be the primary factor. If you were designing for them, then you'd flatten profession balance and remove the uniqueness and individuality between professions. They all need to be relatively strong in all forms of attack and defence in order that the player's skill comes out as the major deciding factor.
But this isn't true of all games. In some games, they have leagues for small teams of 2 or 3 players, which are the primary status goal for PvPers. Those games can be balanced with more holes in offence or defence of classes because these are then balanced out by your team-mates. Certain class combinations are certainly seen as the 'best', but different combinations are feasible and are played.
There are also games where collision detection is on for players, ranged can shoot their own side if they're in the way, hills/water affect speed of movement and LOS is handled better allowing hiding etc... which actually enables battle tactics and strategy at a mass level. Many people then find this to be their goal play.
It turns out that quite a lot of players enjoy and want to play a more co-operative team or group focussed PvP. This is understandable in a gaming environment where the focus is (should be) on coming together as groups whether that be teams or orgs. But in AO's PvP there has, in the past, been a tendency for one-on-one play to be paramount with super-twinks ruling the roost, which has estranged many players from PvP. This is one of the downsides of creating a system where individual character excellence and power through twinking is possible. In PvP, the mix had swung too far in one direction.
AO is built on the paradigm of character differentiation. The idea of the mix between a skills based and a class based system is to have class distinctions which control uniqueness while still allowing for individual excellence through character building, twinking etc. It's a system that tries to get the best of both worlds and is generally pretty good at doing so. The mix tends towards the teaming side of things, primarily because of PvM - but even there, there's a need for balancing to allow for soloing too, so the mix can't tip too much to the side of teaming. In PvM though, the designers have control over the mobs and thus are more able to balance that mix better.
But when it comes to PvP in particular, it's a weak system because the two approaches that AO tries to meld together, need to be managed very differently. One pushes all the time toward making the professions as similar as possible - the other pushes toward them having holes in their templates that need to be filled in by team mates. In the past, AO's PvP has pushed much more toward the twinked one-on-one player, built as an all-rounder - often in spite of the desires and designs of the devs.
I think that what FC have been doing in recent years isn't far off the mark. They've been trying to encourage more team play in PvP. So they've been balancing more toward there being holes in the templates for the professions that are best filled by other players. They've done this not only through profession design, but also by introducing new Titles, the BS environment etc... and by trying to draw more players with a broader motivation into PvP through VPs.
But for those core, dedicated AO PvPers whose motivations are more based on the status attached to individual skill and excellence, that is problematic. Perhaps, there should be a league system like in some other games, where specific duos or trios form long-term teams that move up and down a ladder based on some points system which includes the position on the ladder of the opponents you kill as a factor in how many points you get.
That may go some way to allowing these players to have the status associated with personal excellence while still being based in a team game, balanced as such.
Just my two penn'orth and musings,
X