I seriously don't understand why this hasn't been fixed, BiS accessories for tanks should not be crafted gear 20 ilevels under cap that cost millions of gil to buy and pentameld. It's not good design, hurts pretty much all players, and is unfair to tank players compared with other roles.
The fix I would suggest would to make accessories have a CAPPED amount of strength (yes, you shouldn't have to meld strength either, all other roles can customize their accessory melds) equivalent to the current max you can get with a STR VI meld, and then simply make that number increase by 5 or 6 every 10 ilevels.
I really don't see this being at all difficult to fix, there's barely any number crunching involved and it probably amounts to a few lines of code at most as it's just a number which will have a flat percentage effect on tank dps and will require no ability or potency tuning.