Didn't have time to respond to this yesterday.
I'm not too sure where to start with this as the criticism makes no sense to me. Leaving aside the Dutch / Ajax teams for a second, we've literally see the success of false #9 systems in the past decade with a number of different teams who all managed to 'get behind the defence' - most obviously Barcelona in which Messi and co were rattling in around a hundred goals a season playing a false #9 system. The penetration comes from a number of players, primarily the front three i.e. the wingers and the false #9 himself. You can play as a false #9 and still get in behind the defence. The tactic doesn't literally mean that the central forward is constantly playing in midfield.
Along with Messi and Barca another example is the 06/07 Roma side in which Totti moved from being a #10/trequartista, to being the furthest forward player on the pitch whilst still acting as the side's offensive playmaker (dropping deeper to pick up possession). In that false #9 role Totti scored over 30 goals.
In terms of our team, the penetration would be coming from a number of players, including Wilkes, Gullit, Van Hanegem, Neeskens.. and most importantly Cruyff himself. As I said with Messi, Cruyff playing a roaming free role doesn't mean he's not going to get behind the defence. Look at his goal against Argentina in '74 where he breaks past the centre back to collect Van Hanegem's chipped through ball - that's classic penetrating forward play.
As I posted in the thread his goalscoring record is actually superior to Rummenigge's and he did all that playing in the same false #9 position. Ajax in the early 70s were scoring 100+ goals each season and the Dutch were free-flowing goalscorers in '74 whilst operating in the same tactical set up.
