The "Perfidious Albion" wasn't known for its righteousness either. No great power is trustworthy.
Germany's position as the dominant power on the continent just wasn't acceptable. It just happened to be Germany, but it could just as well be USSR, France, Italy, Bulgaria or even Luxembourg for what is worth.
This misses the point and also fails to understand that "Perfidious Albion" isn't actually an insult at Britain for failing to keep to treaties. It's actually an insult that, while going back to the 13th Century in general back then with the whole being on alternating sides plus the whole Norman leadership technically being constantly treasonous vassals of France.
The modern usage stems from betrayed French Revolutionaries who saw Britain not really caring when they were proposing a consitutional monarchy withdraw the vague noises of backing when they killed the king and chose a Republic.
Britain didn't actually have a history of betraying European Treaties by the 20th Century. Colonial ones on the other hand?, more "altering the deals" but still a bit "Perfidious".
But to get back onto the point,
Britain's reputation was not Churchill/Chamberlain's just like Germany's reputation was not Hitler's
If Hitler was replaced, then any deal offered could be expected to be held for the average amount of time, a few years to a decade. Two, at most.
A deal made with Hitler is worth less than the paper it was written on because Hitler showed that he would not even keep to any treaty for a few months.
Quite frankly, a peace treaty signed with Hitler would collapse any government in any country that accepted it simply because of the complete lack of trust anybody outside of Germany had in him.
Edit: Point of this rambling post is that there are two reputations that matter in diplomacy, the Country's and the Leader's. A bad reputation of the former tells people that you won't get anything long term out of them whereas a bad reputation of the latter tells you that you won't get any commitment to what they say out of them, it will in fact just be lies that will be abandoned the moment it is convenient.