Very much so. The Poles had 37 divisions to the Germans' 70, and each German division was much stronger. Poland's entire military budget from 35-39 was less than the Germans had spent on just the Luftwaffe in 39. It was a horrendous mismatch. They had absolutely no illusions about what would happen if they were left to fight Germany alone. Hence their plan for defence relied on the alliance with France (and to a lesser extent Britain).
The French had promised a full-scale invasion of Germany within 15 days, and Britain promised immediate intensive bombing of German military targets by the RAF. And yes, the RN would obviously be in a position to implement a blockade, although the usefulness of that to Poland was questionable.This was what the Poles believed would happen, because it's what we promised them. As you say, what materialised was bugger all apart from the Saar Offensive, if you could even call it an offensive rather than a bit of a probe. I do wonder if the Saar Offensive was a cynical ploy to allow the French to say they satisfied their treaty obligations without doing anything actually useful.
We seem to have taken the decision not to launch the full-scale attack on Germany on the 12th Sept at a conference with the French (and indeed to pull back from the Saar operation). The following day we told the Poles the big offensive would still go ahead but had been pushed back to the 20th. That would appear to have been a straight-up lie.
Britain and France could have sent 110 divisions against the 23 that the Germans had holding their western border. If the attack had come before the Soviets had hit the Poles from the east on the 17th it's certain that a large part of the German force in Poland would have been rushed to the west. Would the Soviets have cancelled their land-grab if they had? Who knows. German Generals thought they could maybe hold the British and French for at most a week with what they had in the west. It's all a bit "what if" and we can't say for certain we could have saved Poland (so much depends on the Soviets), but it's clear that by taking the decision to do nothing we allowed Germany a free hand to finish what it started.
We also actively worked to undermine Polish readiness in the pre-war period, the British and French governments thought that any overt preparations the Poles made (such as beginning mobilisation) would be too provocative. The whole policy of the Chamberlain government towards Poland was shockingly inept and ineffective.