The impact of Superior Will can also come from monster powers where saves cascade. For example, in one encounter, there were two Yochol Tempters.
Seductive Glare (minor 1/round; recharges when the target
saves) • Charm, Reliable
Ranged 10; +23 vs. Will; the target is dazed (save ends). First
- JILED Saving Throw: The target is stunned (save ends). Second
-ailed Saving Throw: The target is dominated (save ends).
The character with Superior Will has to fail 2 saves (the bonus save, and then the normal save) to become stunned, so besides the initial defense bonus, having the feat is cutting the chance of stun in half, as well as vastly reducing the chance of dominate.
Because the feat bonuses in Essentials are so high compared to the original core feats and the fact that they can be purchased at level one, it changes the balance of the game system. There used to be a significant NAD penalty in at least one defense for taking a 20 stat PC. Now that main penalty can be negated at level one with a single feat. Just another illustration of how Essential feats are overly potent.
Player: "I want semi-decent Defenses for my Fighter."
Core DM: "Put an 18(16) in Str, a 14 in Dex, and a 14 in Wis. AC 19, Fort 16, Reflex 12, Will 12"
Esentials DM: "Put a 20 in Str, a 10 in Dex, and a 14 in Wis and take Lightning Reflexes. You get the same defenses: AC 19, Fort 16, Reflex 12, Will 12, but you also get the equivalent of taking the Weapon Focus and the Expertise feats for the cost of a single feat. And, you can still take both of those feats later on."
This isn't game breaking, but it sure as heck is more potent than before the Essentials feats and the errata to the core feats.
Emphasis mine.
You know what? Screw level one. Of course things look skewed when characters are basically incomplete - even things that are core or obvious to take are often delayed at level 1.
A fighter wanting to emphasize his non AC defenses will want roughly the same stuff whether or not he starts with an 18 or 20. Once they both have more than one feat, they can both have their expertise, defense boosters, etc. The real difference is still, as always, whether or not you want the +1 attack and damage, or the defenses+other stuff (mostly feat access).
Your core fighter can get Heavy Blade Expertise, Shield Expertise, or the Scale armor feats and is close to qualifying for Heavy Blade Mastery. STR+WIS sets the Essentials Fighter up for what? Polearm stuff? The core stat spread can take Polearm Momentum quickly with his higher dex, and then combo Hvy Blade Expertise with Polearm Gambit. With access to the same feats, the more even stat spread could pick up Superior Reflexes instead of Lightning Reflexes.
Your supposedly same thing but improved Essentials stat spread is hardly unambiguously superior outside of a fleeting moment. At level 4-7, a 17 starting stat dominates an 18 starting stat, which doesn't change that the 18 starting offers some advantages a lot of the time.
While I hate to sound like I'm contradicting myself - since I do feel like Essentials feats usually outshine other feats that exist in the same niche - a lot of core feats are really awesome. Frost Cheese is core. Polearm Gambit is core. Etc. If you're going to compare pure Essentials characters with pure PHB 1 characters, then of course the Essentials characters are going to have bigger numbers. However, they'll be lacking in other areas and options. Heck, the whole point of Essentials stuff like the Slayer is to gut the options of the class in exchange for consistent bigger numbers.
PS: Based on the ACs of your fighters, they're using Scale+Shield. So they should have 14 Ref instead of 12.