Yes, that's what's impossible to do without messing up their Army and failing to defeat Poland, let alone France.
What is achievable given their resources? Is there anything that a forward-looking* General Staff and OKW could do in the way of plans and preparation? With minimal resource demands.
I suspect answer is "nothing that raises Sealion from totally impossible to almost feasible". But how do we prove that to everyone's satisfaction?
*OK, also close to ASB for the Nazis.
The reason Sea Lion is so fascinating is that it is not - technically - ASB:
The Luftwaffe could
win the Battle of Britain.
The KM could
force a sea corridor across the channel.
The army could
get an expeditionary force to the south coast of England.
keep the corridor open and the army supplied.
The invasion force could
reach London and could
take Britain out of the war.
This all could
be done without wrecking the German ability to wage war.
The first is the only one with a reasonable chance, the rest are absurdly unlikely, and the last is the kicker: "Mein Fuhrer, a plunder economy is all fine and good, nations have been doing that for uncounted years, but seized crops in farmlands and seized mining output is doing no one any good if it can't be moved to the workers and factories!"
Also, lets not just call the Nazis stupid and let it go. Nazi ideology certainly didn't help, and many mistakes were made, but "Good idea, but Jerry would never think of that" dismissal doesn't help. (And to be fair, staffing the British command with a bunch of Nigel Bruce stereotype duffers isn't all that great an idea either).
The problem with any answers to the question of "What could Germany have done different?" is that Britain would have changed production in response. For example, Germany produces a fleet of E-boats? Britain would invest in more destroyers. More U-boats? More ASW. etc