Not only trying to balance out the higher-tier items is an issue with the whole ports armours but I also think that we should take a look at lower tier items as well for balance out the economy.
1. Barrows/Chatoics: These two class sets of items are some of the most common items people use in an RSPS when getting started and from my personal perspective they don't do enough to lower tier bosses. I feel that these two items should have some sort of buff too them that makes them more usable at low-tier bossing and even some Mid-tier bossing like GWD.
2. GWD: GWD needs a bit of a revamp with set timers for all the bosses(Excluding Nex Of course) and on top of the set spawn timer the two bigger bosses in GWD that people fight Bandos and Arma needs a slight nerf. Bandos being that his defence is too high for lower tier gear to really hit well and or consistently on and Arma being a damage nerd because even when I go there in higher tier gear Arma can still do a fair amount of damage to you along with the minions. Sara is generally fine where she stands not too hard and too easy. Zammy is fairly fine where he stands but he doesnt really get much attention since his drops are pretty lack luster since the ZSpear had a speed nerf awhile back making him a pretty pointless boss to camp. Overall on this is having each boss have same respawn timer. Giving bandos a Defence nerd, Arma and Minions a slight damage nerd. And making the Zspear a bit more usable in game.
3. Ports V.S. Nex Armour: Ports is extremely over powered in the the light that is extremely cheap, Can start at early game, and can be traded and upgraded. Everything about ports needs an overall nerd from stats to making all of ports untraceable period. Something slightly less unnecessary would possible be giving a buff to the Nex Amours (Not Really Needed but could be played around with) Just to keep the appeal on them over using ports armour.
This is just some of my personal opinions on how I think things could help stabilize the economy a bit not really sure if they would work but you won't know until you try.