“Arsenal has been financially constrained over the years because of the club’s move to the new stadium”.
Is it a myth?
No.

The last Deloitte’s “Annual Review of Football Finance” shows the following figures spent by clubs:

Wages 04/05-08/09
See here

The season by season breakdown can be found here

Net transfers 04/05-08/09
See here

Wages plus net transfers 04/05-08/09
See here

Deloitte is not talking about “money available”, it is talking about “money spent”. Could you spend unavailable money?

During this five year period the clubs won:

ManUtd - 9 trophies (EPL 06/07, 07/08 & 08/09, CL 07/08, LCup 05/06 & 08/09, Community Shields 07, 08, World Club Championship 08)

Chelsea - 7 trophies (EPL 04/05 & 05/06, FA Cup 06/07 & 08/09, LCup 04/05 & 06/07, Community Shields 05)

Arsenal - 1 trophy (FA Cup 04/05)

Liverpool - 4 trophies (CL 04/05, FA Cup 05/06, Community Shield 06, European Super Cup 05)

Tottenham - 1 trophy (LCup 08)

So the for each trophy the round cost in round figures is:
ManUtd £58m.
Liverpool £138m.
Chelsea £143m.
Tottenham £312m.
Arsenal £480m.

This is the sport efficiency of the leading English clubs.
The most efficient manager is Sir Alex Ferguson, the worst – Arsene Wenger
And Man Utd spent only 8.5% more than Arsenal.

Therefore the notion that “Arsenal has been financially constrained over the years because of the club’s move to the new stadium” is not a myth. It is a falsehood. Produced by Arsene Wenger in excuse of his own lack of sport efficiency.