I don't think this is true if you consider limited spells slots, subclass abilities and fighting style. Subclasses and fighting style for the most part boost damage or boost tankability or both while most wizard subclasses do not do that.
Wizards also can't do 95% of the tankability if they focus on damage. It really is either-or. They can do over 95% of the tankability if they focus on defense (probably over 100% on a bladesinger given equal constitution in tier 2), but their damage will suffer, because to keep the edge in tankability they need to use spells like blur instead of spells like shadowblade.
It is less of a loss than you might think, because
shield is so strong, and a first-level spell, something you graduate out of quickly for damage-dealing potential, meaning you can start spending them on such one-off uses more casually in short order. It also gets horrifically worse at the highest levels, because at level 18, you can turn one each of your 1st- and 2nd-level spells into at-wills. Having
shield at-will is ridiculously powerful, since you have effectively +5 AC
all the time, and that's AC that stacks with
all other sources. Your other spell can then be
scorching ray (or
Aganazzar's scorcher for wider AoE) if you want always-on offensive capability, or a more flexible defense-and-utility spell, such as
invisibility or
levitate. And you can change these spells with every long rest.
Known and accepted problem? I don't agree that "wizards are way too strong." I think they are one of the stronger classes. So are fighters. Who are easily the most popular class in 5e, from everything we've seen. I think there are a few people on this forum who take every opportunity to argue for fighters and against wizards, but that isn't really evidence of anything, except that there are a few people with some strong opinions on the subject. Which, more power to 'em.
Popularity doesn't make something good. Almost everyone who's done any degree of optimization of the Fighter in 3.X agrees it sucks. It's also
one of the most popular 3.X classes. Because the Fighter is
always one of the most popular classes. Fighter is
always popular--often the MOST popular--regardless of edition. Every single time.
Likewise, the 5e dragonborn is agreed by almost everyone--even WotC at this point!--to be one of the weakest races in the PHB. Which is why we got straight-up replacements in the gem, chromatic, and metallic variations. Yet, even before any of these extra options arrived, dragonborn had done nothing but grow--eventually becoming the 3rd most popular non-human race, after half-elf and elf, managing to overtake even the sexy bad-boy/bad-girl tieflings.
All of which are mechanically superior to the dragonborn by a pretty substantial margin.
Popularity is totally orthogonal to power. Some powerful things will be popular, especially true of feats, e.g. Lucky, PM, SS, Elven Accuracy. Some powerful things will be unpopular, e.g. Druid, esp. Land/Moon. Some inherently-popular things will be powerful e.g. half-elf. Already covered that some weak things can be popular. And then some weak things will be unpopular, e.g. spells are particularly prone to this--there are a lot of massively over-specialized spells that almost never get taken, let alone cast. Whether something is
popular tells you nothing at all about whether it is well-made or not.
The Pinto was popular, and also badly designed.