FrogReaver
The most respectful and polite poster ever
I don't know who made that claim, but my guess is by looking at "power" mainly as "killing power", and not including utility etc in "power".
In short: the sorcerer might fall short compared to a true wizard. But comes across as very strong compared to, say, an Archer Fighter. They don't just stand there, they shoot somebody; the Sorcerer just does it frighteningly well. And many more times than WotC wants to admit, there is no real cost involved.
At level 5 the sorcerer is barely better at killing things fast than a wizard. You don't even have the slots or sorcery points to use a big strong spells and bonus action cantrip attacks to kill things faster more than 3ish times per day (and that takes nearly all your resources). At some point you may, but not at level 5.