I'll start with the last point and work backwards.
Belgium's unexpected decision to opt for neutrality can't be simply disregarded as a point for why appeasement was maintained, especially in '37 and '38.
The plan had been to confront German aggression either on German soil, with the Maginot Line to fall back on, or on Belgian soil with the line as an interleave.
With Belgian neutrality, this plan became instantly defunct and the strategies in place needed to be adapted, with the Maginot line hurriedly becoming extended.
This would take to 1942 at the earliest, with greater costs (water table and other issues) and to a lower standard than the additional line - all well known to the gov.
Observers weren't even allowed within side Belgium and as such temporary appeasement was an answer by both governments to aid mobilisation et al.
You then mention the ol' quantitative advantage, which totally ignores the mass qualitative deficiencies in both equipment, doctrine and interaction been branches.
While you rightly mention German tactical advantages being a pivotal factor for success, this was well known by British observes (at least) way before 1939.
Yes German tanks had weaker guns and less armour, but their high top speed was a key part to their doctrine as mentioned in Guderian's Panzer - Achtung.
They were centralised in divisional/brigade structures, whereas British and French with their heavier cruiser tanks or low-speed infantry tanks were spread thing.
Infantry divisions/brigades were in turn were far better equipped than their British and French counterparts: number of MG, artillery, mortars, infantry vehicles etc.
We went to battle in '39/40 with the 18 pounder and 4.5inch howizter, which were all pre-1914: great in their day, but not so good when it came to the late 30s.
Now, not all the German artillery weapons were new, however there was a much better mix of new and antiquated heavy weapons, again all tied into their doctrine.
I could go on and on here, with the Luftwaffe having higher numbers of quality aircraft versus our own, or how the Kriegsmarine's ignorance of the WNT giving help.
Where we did have numerical advantage, the quality of aircraft was questionable at best: look at the Blenheim. Importantly, they had a sizeable fighter advantage.
While being much larger in actual manpower, the French army was a shell of its once brilliant self, with poor discipline, training, equipment and mobility.
Yes they started from a lower base, however their blatant disregard for treaties and limitation gave a great advantage: they were building the Bismark vs. our KGV.
Tactically, it isn't as simple as making a mass change and the advancements that were started again would not come to fruition until 1941-43 at the earliest.
Could or should we have done better to stop the Germans in 1940? Could or should be have rearmed quicker and ensured our doctrine was better?
Yes, however that doesn't negate the understanding that pre-war we were behind them, which we knew it and they knew. In 19490, this was still the clear case.
Therefore, an option was to use our considerable resources to try and match their strength over time, as we couldn't afford it quickly. Here comes appeasement.
With regards to the leniency, I recommend you read Catherine Cline or Maynard Keyne's views of the treaty. Woodrow Wilson publicly declared it was so.
Appeasement did not work, that's clear to see and we could have done a lot more as well; but, the logic behind it had many, many merits and it still does.
