And they were always going to stop the Axis roughly at Alamein. Practically every time. Only in a geographic sense were they near Alexandria - in reality his Afrika Korps culminated well and truly short. As any decent analysis of the stratigic situation of the Mediterranean and Germany at large should have told Rommel it would.
Rommel's attack on Egypt was never anything more then a foolish waste and again shows the total failure of the German system of strategic planning and means/ends analysis.
Actually the German system of strategic planning and analysis, they sent a general officer (Paullus?) to North Africa just after Operation Compass, who recommended that a blocking force be sent to preserve The Italian empire in Lybia but that the logistics were impossible for a campin of conquest in Egypt.
Rommel of course ignored that and proved him correct.
Looking at the battles of First Alemein a few points come to mind,
One is that it was not an unflankable position as the 8th army had too few troops to defend the whole front. However Rommel had too little petrol to attempt a wide outflanking manoeuvre, so the battle settled into attritional warfare around The various Ridge lines.
Rommel had lost his Edge which was the " good source". Colonel Bonner Fellers messages.
Finally Alexandria as a port
The main constraint on axis supply operations assuming the capture of Alexandria is that British air power would make it unsuitable for use.
Or only by small costal craft .
Regards Hipper