Statistics aren't everything obviously, but if you do the Transfermarkt player comparison thing they are essentially identical. Garnacho has a goal contribution every 344 minutes, Brennan every 339 minutes. Roughly speaking one goal or assist every 4 games.
Some players we are linked with have better stats ... e.g. Cunha every 212 minutes, Bryan Mbeumo every 277 minutes, so Cunha is not far off a goal or assist every other game. Some are much worse though - Gibbs-White every 569 minutes.