How can I prevent casters from stealing the spotlight from non-casters?

I have been running a game of D&D and the group is split with two non magic users (Fighter, Barbarian), one quarter-caster (Paladin), one half-caster (Bard), and two full casters (Cleric, Wizard). The game was going rather well as I had started them from level one, however the group has reached level five and the wizard and the cleric have started solving everything which has been making everyone grumpy. Wizard summons are better at tanking than the barbarian and Paladin. Cleric is far better at buffing the party and talking compared to the bard.

I don’t wish to just go, “You guys walk into a dead magic zone. None of your fancy magic works now.” What can I do to distribute the spotlight equally among the party members?

I was asked for examples. For prime example whenever there is a combat encounter the wizard casts alter self to gain a high natural armor combined with mage armor causing the wizard to have an AC equal to the paladin removing the whole squishiness disadvantage. The wizard also has spell focus conjuration and augment summon so his creatures are actually as good as the fighter and paladin during combat situation.

As for the cleric he has the divine metamagic feat focusing on persistent spell so he is able to give out two buffs that last all day long so the bards song bonuses are pretty much negligible.