Unready Britain
Unready France
Soviets right after the Purges
Czechoslavia
vs
Unready Germany
Even if the old Entente buddies aren't prepared, neither are the Germans.
True. And now all you have to do is go back in time and
tell Britain, France, etc. that Germany - which has just spent the last few years in a big propaganda campaing of how
ready it is - is just as "unprepared" as they are.
Or, IOW, they didn't know. And weren't willing to risk it even if they suspected.
Look, you're running country "A". You know you aren't ready for a big war and the only way you can see to stop country "B" is to, well, fight a big war. Now country "B"
may be just as unready as you are - but you don't know for sure. So your choices are to:
a) Fight now, knowing you're unready and
hoping they are too.
b) Fight later, knowing that
then you
will be ready, even if
you're giving "B" a chance to ready themselves too (that is, if they
aren't already).
Given Britain and France
know they can outproduce Germany in war materials, any "contest" where they delay the war helps them and hurts Germany. Delaying it as long as possible (even if it means "appeasement" in Czechoslavia - who's other choice in your scenario apparently is to be the battlefield for Europe...which I suspect they don't consider to be an upgrade from appeasement) is therefore in your interest.
Hindsight is a wonderful way to make decisions...unfortunately, it only works long after the decision has to be made.