Right—it's not like they'd have done better without it. Odds are they would have lost even sooner, in fact. The little air war after Poland was invaded would have instantly been a bloody ground war in the West, too, rather than most of the action on that front waiting until Germany marched through the low countries. Not like they'd have been better off with that border unfortified—it likely bought them some weeks or months, not that it mattered for the ultimate outcome. Hell, without it, Germany may have decided to attack West first, then turn East, rather than vice-versa.