Not necessarily so. The main point of the formation was that if you keep attacking, the other side would be shut out and thus couldn't play a counter attack. Also, despite having two centre backs, the two half backs in the middle, along with the central player would come back when the other team attacked essentially creating a defensive back five. It was a formation like this that helped people like Stanley Matthews and Puskas being the greats they are referred to today.
But it's not just that, the idea of football at that time, was to out score your opponent, something I and many others believe football should be about. The stance now is "Don't concede". I've spoken to a few folk about this set up, one who played as a winger for Caley and Thistle and he swears that this system was by far the best, the most entertaining and the most effective.
How effective would the 2-3-5 and other old formation like the W-M and the 4-2-4 today? It's hard to say. I saw a good analogy on this in a discussion on football tactics on P&B. One poster was talking about how new tactics arise in countries that are mainly isolated from the outside world. An example of this is North Korea, who, during the Asian World Cup Qualifiers often set up their team in the 3-3-3-1 formation - something that is indeed very unusual. The analogy the poster used, was that at times highly technologically advanced countries like America and Britain have trouble adapting to fighting against groups like al Qaeda, due to the fact they use far less technology and still use many old fashioned ways of living and fighting. The same could be said for football. If a team were to line up in an old fashioned formation with old fashioned tactics (in this case for arguments sake, the 2-3-5), the opposition may find it difficult to beat that team due to their lack of knowledge on how to beat that system.
So there you are, but that's for another thread.