My group is three full casters and one half caster. Up to 14th level now.
Lore Bard.
Abjurer Wizard.
Light Cleric.
Paladin.
We don't have issues with concentration.
For one, a lot of really great Wizard self buffs do not require concentration, while at the same time making you harder to hit.
Secondly, maybe next time you should try an Abjurer Wizard. They get an Arcane Ward, and when your Ward takes damage you don't have to roll concentration. In fact, I hardly ever actually damage the Wizard.
Where you popping shield? You should be quite hard to hit with shield.
Do you play grid or ToM? If you use grid you should be able to stay out of enemy Line of Sight often. There's nothing in the rules that state you must have LoS to concentrate, so go around a corner!
Also funnily enough the list of spells that require concentration at higher levels is actually pretty low. Look at Force Cage for example. The spells that require concentration are vastly outnumbered by those that don't at the higher levels.
Concentration is a tactical choice.
It's a shame you retired the Wizard, the Wizard in our party is extremely powerful. He is a massive force multiplier for the group, and concentration doesn't get in his way.
I think a lot of this depends on the type of encounters that the DM throws at a group of players. A DM with a lot of foes, and possibly surrounded or possibly with ranged attacks, and a lot of weaker attacks? Concentration gets broken a lot more often. A DM who has fights with fewer foes and the foes fight toe to toe with the front line melee PCs, concentration gets broken a lot less often.
My experience (and a reason I started this thread) is that concentration is a pita. It seriously hampers which spells can be used and handcuffs players into not being able to use many of their options.
In fact, based on what I have read about how many other groups have casters take the Resilient Con feat or the Warcaster feat, I might remove the penalties in my house rule for multiple concentration spells in the first post of this thread in my game. It just seems like a rule designed to tick players off.
Concentration is just on SO many spells that it leeches the joy out of having cool spell tactics when playing a spell caster.
Player: "Oh yeah, I cannot put Fly on the fighter to get him to the flying creatures and cast Hold Monster on the BBEG."

Spell casting tactics in 5E are extremely simplistic in nature because casters are not allowed to cast any spell at any time. If that is some player's cup of tea, fine. But I think it is lame. It sucks the fun out of playing a caster.