Which was the entire point of the line. Belgium back out if their defense deal with France, and even German high command was pissed about how quickly Rommel was going through Northern France. Fall Gelb was absolutely balls to the wall insane and could have seen the German Panzers encircled if the Allied forces had been the least bit competent.
100%. The British army, at the time, was good for little more than putting down colonial rebellions against vastly inferiors foes.
Tbf to them though, at the time, no one had any reason to expect hundreds of mobile artillery fortresses, driven by methed out nazis, to appear 50 miles behind them.
It was more about resources. The allies were basically the rest of the world between the British, French, and Dutch empires. Japan did more to disrupt that than Germany did, and Germany was eventually knocked out of the Naval war, which left Britain free to import as much as they needed from those combined empires. And the Nazis were running out of fuel, which is why they invaded USSR.
WWII ended up being a war of attrition just like WWI was, the main difference was that Germany was able to take a lot more territory before their lack of resources caught up with them.
The Nazis were winning for most of the war. The UK might have been knocked out of the war entirely if the Nazis hadn't paused their advance and given them a chance to get their men back across the channel, which they needed to borrow civilian boats to do.