Rommel was sent in with the (new minted) Afrika Korps because the previous administration (Wavell, Wilson and O'Connor) had been having so much success against the Italians. It's doubtful whether Rommel would have had quite as much success as he had if O'Connor had been left to use his troops in North Africa, but significant portions of his command were sent (uselessly) to Greece and (needfully) to the Far East. Wavell was replaced by Auchinleck. There were several changes of middle command with Auchinleck taking over 8th army himself on a couple of occasions. Gott was due to take over 8th Army under Alexander but was killed in Egypt (he was the one who was shot down). Alexander did replace Auchinleck as Commander Middle East and Montgomery was given command of 8th Army.