Where is that "good argument" substantiated?
People say exactly the same thing about IQ tests, probably because it's something they'd like to be true. But it's not backed up by the evidence.
There probably is a decent correlation between cognitive ability and performance on these tasks, but it’s obviously mediated by practice.
If you think I am an unreliable source, why don't you look at the other meta-analyses like Melby-Lervåg, or Sala? Or look at the criticisms made by researchers like Redick whose experiments turned out to be nulls? (Redick's most recent comment on DNB is titled "The Hype Cycle of Working Memory Training" https://journals.sagepub.com/eprint/U8YNVXKM5SKF6ZY9TQBR/ful... , so you can probably guess what he thinks of DNB now.) Or look at what the field thinks in recent studies - assuming you can find any recent DNB/IQ studies, as everyone has realized that it doesn't do anything.