Here's the main problem. It seems like the developers want to widen the damage gap between tanks and dps. Players, on the other hand, generally like to do as much damage as possible.
Every problem that we've had relating to tank accessories this expansion comes from this. At the start of this expansion, this was done by removing VIT from the new gear. The developers had created a damage gap. Ordinarily, that would have been the end of the discussion, and tanks would be doing less damage than even healers. (Remember Patch 4.01: What was that? You say that you want more enmity? You say that the lack of STR on your gear is interfering with your enmity? I'm struggling to hear you, but it sounded like you said enmity, not damage. Here, have some more enmity.)
Players quickly realised that their new accessories were doing less damage than their old i270 pieces. Surprise, surprise, players started forgoing the new accessories in favour of the ones with STR. Uh-oh.
Consider the following:
Letter from the Producer LIVE Part XXXVII Digest (8/10/2017)
To dissuade players from using the older accessories, they had to put a minimum amount of STR on the gear. So now STR goes up by a couple of points every 10 ilevels. You still want to use the newer accessories because they're marginally better, but your damage doesn't get significantly better with newer gear. That should have been the end of the discussion. Except for one thing.
Primary attributes are supposed to dictate the power difference between gear at different ilevels. When the STR difference is outweighed by secondary stats like direct hit and crit, those stats instead dictate gear strength. Because the STR difference between gear levels was too small, you had lower ilevel gear pieces which gave you a bigger dps benefit. Enter crafted gear.
This is a similar problem to what was happening with dead stat-weighted attributes like Parry and Accuracy on tank gear pre-Stormblood, in that there was a wide variation in secondary stats within a given gear level. So you would run into situations where lower ilevel gear outperformed higher ilevel gear, because it had less Parry and Accuracy.
Here's where we're at now:
Letter from the Producer LIVE XLII Digest (2/27/2018)
It seems like we're hitting our heads against the same wall. The developers aren't asking "How do we give tanks meaningful gear progression with higher ilevel." The question they're asking instead is "How do we limit the power of lower ilevel crafted gear."
Removing access to Direct Hit melds in 4.4 isn't going to solve the problem. Crit is probably going to be a better stat by that point (it already is for WAR, especially after the 4.2 changes). You're just going to see crafted gear with Crit/Det melds instead. In order for raid/token accessories to be preferred, the primary stat gain has to outweigh the higher amount of secondary stats on the crafted gear.
The bottom line is this. Players want meaningful stat progression on their gear. If you pick up a new, higher level accessory, you want it to make you stronger (i.e. more damage). In order to do this, there has to be a big enough separation between ilevels through primary stat gains to outweigh any variations in secondary stats within a given ilevel.
What do I see as the solution? Well, look at healers. Healers don't use INT. You don't have to worry that boosting the amount of primary stats on Healer gear is going to encroach on caster dps. You can tune them independently of each other. Instead, you have a primary stat that boosts both healing power and damage output. Perfect.
Do the same thing for tanks, next expansion. Make tenacity into the new tank primary, and have it boost damage output, self-healing, and mitigation. Have it scale at an appropriate rate, such that it doesn't get overpowered by secondary stats. That way, you can tune tank damage output without worrying about them encroaching on melee dps output, because they would have different primary stats.