What you see as an issue, I see as a squad well balanced between experience and youth.
Players older than 30:
Howard; Hibbert, Jagielka, Distin, Alcaraz, Barry, Osman, Pienaar; Kone - 9
Players younger than 30:
Robles; Baines, Oviedo, Coleman, Stones; Gibson, McGeady, Mirallas, McCarthy, Besic, Barkley; Lukaku, Naismith - 13
There are a few more youngsters who may step up too.
I made this point elsewhere
Name Age App
Jagielka 31 30
Kone 30 5
Distin 36 37
Barry 33 37
Osman 33 43
Pienaar 32 25
Howard 35 37
Alcaraz 32 7
Hibbert 33 6
Baines 30* 35
*30 in December
10 then, as I am including Baines who will be 30 before the next transfer window. 262 appearances between them last season, nearly half the squads total for the season (the rest made 301)
In terms of play you might see that as balanced, but from an accounts point of view its dangerous. Those 10 players are the core of the team but will begin to (have begun to) deteriorate as players. It will require major investment to overhaul the squad, money Everton don't have. They had a real chance this summer to start improving the squad for the long term this summer, before the market fully adjusted to new economic realities of the TV deal. However, they spent all their money in one go to field more or less the same team as least year (but one year older)
Sure, they might be ok this season, they might even do well next season, but the mid to long term is problematic and unlike United (who coasted along with an aging squad until all their chickens came home to roost last season) they don't have the finances to just go out and buy the players they need. My argument then is from an economic perspective, not a playing perspective. Sure the kids might come good, but realistically how many do you expect to come through? 10? Because you might need 10. And don't forget Everton have been paying off the clubs debts by selling their best, young talent for years now.
I just think your idea that the team is well-balanced is a tad short-sighted.