So funnily enough i would say instead of dual wielding, rangers are better off using sword and board. (Or axe and board) in melee. As sadly their damage output will not even out the permanent -2 AB they get from dual wielding.
Whereas with shield parry they dont need 3 feats, will have unmodified AB so more chance to hit, and higher AC. (Since any ranger wearing any kind of armour can only start with 5 parry AC! So actually shield parry is even more noticably better.)
You would need to take Medium Armor Proficiency and Shield Parry and lose out on the damage of two high AB attacks per round. If you want to minimize the damage loss you'd need Exotic Weapon Proficiency for a Bastard Sword.
So you still invest three feats for an AC bonus but a damage disadvantage, for a class with the base HP of a flanker. All in all I'd say it's a viable or even choice, but not objectively better. Either way - shields are pretty neat atm, but somewhat niche.
You dont need medium armour proficiency actually. From 17 dex you have the chance to max out your dex bonus with a studded leather armour. Which is not even that hard to achieve/get. (17 dex i mean!) I only wrote that for the shield parry to take maximum effect you should be using at the worst a chain shirt.
The exotic blade argument I can actually accept. However with the missing out of two high AB attack, both of them will have -2 AB in comparison to the single first attack. Sadly there are quite often times when this really matters, and the chance of having an additional 20 roll is something you should not really count on. (I am usually on the receiving end of someone or something rolling massively 20-s against.) The only folks who can make up for the loss of this are usually the sneak mix builds who get more damage dealt out with every hit. And a few other builds, but for rangers going DW is most of the time the wrong choice sadly.(Though parrying 1on1 with someone it can still be very usefull)
Of course I am talking about my own ranger experiences. However it is a bit ridiculous that currently if i took everything into consideration, not even using any kind of hard to find gear (like +1 AC dodge bonus boots and better), a ranger on level 14 with a shield parry build can achive around 60~ish ac on level 14. With same levelled party, and the character would also have evasion.
Back to the damage you mentioned again and the AB difference and exotic weapons.
Whereas true that if you wish to have some damage dealing abilities or decent ones it is better to go with bastard sword or katana, if you really want to do damage, take a two handed weapon. With ram's and bulls str (and occasionally favoured enemy) you can really capitalize on it. It even makes more sense to use two handed weapons in melee if you are focusing on damage dealing than to use DW, simply because of the -2AB. Or use a bow/sling/xbow/throwing axe. Even without the banebow you can dish out pretty good damage with a bow(or the other appropriate weapons.)
In regards of feats, with the recent requirement of rangers required to take FE this means less feats for them to take. More better suited and useful feats than an FE. (FE gives antagonize bonus to rangers....which is still not a ranger skill but that is for another discussion.)
Actually I was really considering to make an elven cleric that will use just a chain shirt and go sword and board to see how powerful it can be. Getting simply 10 AC just from shield parry(of course from later levels) seems to be quite worth it to make chain shirt clerics. And likely you would still have enough ability points left to get divine shield and the other...as to say divine feats most builds have. (or even paladin:)