I think you overestimate Germany’s ability to not get fooled.
Germany was fooled several times-just look at what the Soviets did:
If you’re saying D-Day and the deception in Operation Bagration (and all the other times on the Eastern Front) was all due to betrayal, it should be well known.
In response to your questions, there are several clear answers:
Most German submarines were destroyed by now, and the rest would have been near Pas De Calais, where Germany expected the Allies to land.
And there were German naval units in Normandy-several torpedo boats, or E-boats, which sunk a Norwegian destroyer, the only German naval victory on D-Day. There were also these German naval assets at Normandy: 3 torpedo boats, 29 fast attack craft, and 72 minesweepers. If there truly was sabotage these would have disappeared as well, and the secret traitor would not have been uncovered anyway by the Nazis if we don’t even know his identity today.
The stripping of Luftwaffe and anti aircraft assets were probably done to reinforce the forces in the Defence Of The Reich campaign, after the Big Week which drove German aircraft numbers down to irreplaceable levels:
As for the ordering of targeting devices from Normandy, it’s the same reason why Rommel left for his wife: Inaccurate German weather reports.
As for the two agents or spies your were talking about, one of them was a double agent (like Germany’s entire spy network in Britain), and simply bad luck and quarrelling at higher levels in the German command prevented them from using potentially important information from the other agent.
I cannot find evidence about the problems with the Panzer Lehr Division that you talked about, but I do believe you on this information.
The Allies were much stronger than thought-analysis shows that even if Germany was able to get the full plan from a dead body after the Exercise Tiger disaster (which involved an attack by Germans ships against troops preparing for D-Day), and Germany transferred all of the Fifth Panzer Army to the beaches, and Rommel stayed, the Allies could not have been repelled-shore bombardment and air power would have broken up panzer forces enough to prevent a collapse. The war would have simply lasted longer, or the Soviet would have conquered more of Germany.
Honestly, I find it quite interesting that you came up or mentioned this theory, as it makes for good discussion. I hope we have some great discussions about the German side of D-Day!
Finally, as for the original question, the Fifthteenth Army was eventually used at Normandy, where it was devastated as well as at the Falaise Pocket. The main problem with Operation Market Garden were the Allies not taking seriously Dutch resistance intelligence the fact that German panzer divisions were refitting right where the Allies were going to land. I think if the Fifthteenth Army was at Normandy on the first day, it might have been much harder for the Allies, as they would not have stablished as secured beachheads.