Isn't he just Moura, but a couple of years younger and with no end product?
Even if that's true, that doesn't mean it would be a bad signing. At 20, Moura was one of the biggest prospects in world football and moved to PSG for a similar price, even though he was totally untested in European football. At only one year older, Malcom also has 85 games in the French league, where he's averaged about 1 in 4 (in a pretty brick side side), which is basically what Lucas got in his peak age years at a hyper-dominant PSG.
Also, from what I've read, Malcom's end product is actually supposed to be quite good. Besides his fantastic dribbling numbers, he has a high pass percentage and averages a ton of key passes, expected assists, and touches in the box, which is extra impressive because he's the guy defenses are focused on. Obviously, I wasn't watching a bunch of Bordeaux games last year, but his numbers seem really promising.
However, I do agree with your overall idea that if we're going to spend a ton of money on an attacker, it might make more sense to spend it on someone who is able to play center forward. The more we get linked with these types of players (Pulisic, Zaha, Neres, etc), the more it makes me think that Poch sees Sonny as our full-time, back-up CF, and he wants another creative, pacey attacker to guarantee we lose nothing in our attack when Son moves from the wing to center forward to spell Harry.
Again, I'm not sure it's the best use of resources when we have Lamela and Lucas, but Malcom has the kind of potential that could see him becoming a future star.