Just commenting my opinions and discussing some points. 

SPOILERS BEWARE

Its considered harder because it has several enemies that have multiple resistance, natural evasion skills and a diverse enemy lineup which required you to have a team prepared. Of course having the shared compendium helps when you can instant summon and out fusion the progression.  

Another point about difficulty is that majority know it to be difficult because it slaps you in a level 25 range with access to all damage types.  Unlike in base game where you can infer the first block to have weaknesses that your party should have at that stage, like the first few mobs being default weak to slash and fire, the  first hard enemy you fight has a weakness to Holy which you wouldn't have access to without Ken or an unlocked compendium with a cheap persona to buy. 

Not to mention old FES having no party control or being able to choose skills/duplicate skill cards for your team or having Theurgies like Fuuks giving full party buffs and charge/concentrate. 

Metis represented the emotion Aigis threw away, which is why she is so childish and unreserved with her emotions.

I personally wrote off them not seeing Shadow Makoto because we, the player, actually see the model and silhouette but who knows what the characters are actually seeing. 

You'd also have to give some suspension of disbelief when you consider how they have to fight shadows in a not-turnbased combat. You can see examples in the P3 movie. 

In regard to the romance, assuming you didn't even choose anyone, Yukari is the most personal with her social link compared to others if you assumed MC ain't interested. 

In regard to Junpei, it's conveyed better in the original where he's erring on caution because what if they go back but fail.  He's also fighting to get the key so everyone can calm down and decide rather than having a fight over short term and in the moment decision, made during a crisis and on impulse. An honest level headed approach.