Wlv 16 warrior (Hobgoblin) with a 42 AC:
+14 armor (+5 Armor Spikes Mithral Full Plate)
+7 shield (+5 Arrow Catching, Shield Spikes Mithral Shield Heavy Steel,)
+5 dex
+3 natural armor
+3 deflect.
Haven't checked magic items yet but is it something I should expect on PF?
Your player should have AC 40. Full plate has a MaxDex of +1. So they only get to apply 1 of their 5 Dex bonus to AC. That said, making the armor out of mithral increases its MaxDex by 2, allowing the hobgoblin to apply 3 of their 5 Dex bonus to AC. So despite having +5 for Dex, they only get to use +3. Net result of AC 40.
Full plate (1,500gp) & masterwork (150gp) & armor spikes (50gp) & mithral (9,000gp) & +5 enchantment (25,000gp) = 35,200gp
Heavy steel shield (20gp) & masterwork (150gp) & shield spikes (10gp) & mithral (1,000gp) & +6 in enchantments (36,000gp) = 37,180gp
ring of protection +3 18,000gp
amulet of natural armor +3 18,000gp
Net expenditure: 108,380gp
Wealth-by-level recommends 315,000gp at 16th level. So your player has spent a third of their wealth on armor class and got a 40.
Perspective: a typical raging barbarian will have 16 (BAB) & 12 (STR including a +6 ability enhancement item) & likely a +4 weapon & a good chance of Weapon Focus, able to hit +38. Average dice roll is 10. So the barbarian has a 50/50 chance of hitting AC 48. He literally only misses your hobgoblin by rolling a 1. Rolling a 2 + 38 = 40, a hit. Sure, his second attack only hits a 43
on average leaving him a 70% chance to hit. This third attack drops down to a 45% hit chance and his fourth attack is a measly 20% chance to hit. This means... a typical barbarian is going to still lay down decent damage against your hobgoblin PC. The same applies for fighters, and other to-hit PC classes.
This isn't unreasonable.