If the wizard had more subclasses or spells maybe the class would be better i agree but as it currently stands with the build of game, the wizards are the weakest in my opinion. The one thing they got going for them is basically useless currently (though it might get better but nobody really knows) and they feel like a one and done for the day class for some players which is a bad feeling because in many other games your can go ham with your spells and dish out insane damage each fight, but in BG3 only melee characters in the demo (and the warlock in some cases) deal huge amounts of damage while the cleric and wizard are basically set to heal and occasionally cc’ing enemies due to the limitations of spell slots and the ability to get them back without long resting. This is more then likely going to get better in some way but right now you either have a wizard who does amazing for maybe 1 or 2 fights then is tuckered out for the day, or you have a crowd control only class who dies in a single hit when targeted (which also ruins the cc due to concentration).
Concentration spells do have their problems, hopefully that gets fixed. The Warcaster and Resilient feats will help a lot, when they get implemented. I use mods, so I already have access to them. Warlocks are meant to be single enemy big damage dealers. Sorcerers are meant to cause big damage to large groups of enemies. Clerics buff their allies, inhibit their enemies, and bring up fallen companions when needed. They all can get closer to combat than most spellcasters due to armor and shield proficiencies.
Wizards are meant to control the battlefield. Selectively using their spell slots at the right time. A well place Sleep spell or Grease can change the tide of battle. I'll use Shatter + Sculpt Spells to soften up enemies, and Protect my allies. Web can be very useful to take enemies out of a fight. Also Magic Missile to take down multiple opponents, that my companions have damaged. When the full game releases, and we get 3rd level spells, that is where the Wizard will really shine. Hypnotic Pattern, Fear, Counter Spell, Haste, Slow, Fly, Dispel Magic, not to mention Fireball. More subclasses like Enchanter would be great, but the Wizard is already a very good controller.