Yeah, its been noted. But, the 3 types of shields are not equal.
Ilvl 67 Colossal tower shield. 632 base armor. The best.
ilvl 60 lacquered buckler at 440 is the best Eva shield.
ilvel 66 cardinal round shield at 209/209 is the best eva/ar shield. but notably worse then primaries.
ES hybrids are laughably bad.
harmonic and titanium spirit shields both have 159 ES. titanium has 25% block, and no implicit. so best.
A colossal tower shield could in theory have 3256 ARMOR.
(+400 armor, +110% armor, +42% armor/17% stuck/block recovery.) This would have no life on it. (resists, block, and % life rgen ideal suffix.)
2 to 3 scaling per 15 ar/es. in addition to gem level giving phys scaling.
434 to 651 from armor.+13 to 19 base. Thats pretty insane for a one handed weapon, and shield block/armor.
The crit scaling is not super impressive.
419ES is the BEST possible titanium. (42%es/17%stun/block, 110% es, and +90es)
at, .1% per 10, this gives up 4.19% added crit. to the base 5%. the BEST possible ES shield only gives 9.19% base crit.
Then, the other main weakness is lack of accuracy. Which again will hit that Crit ES shield more.