LH, the 'groundwork' for El Alamein & the Desert Army's advance that followed it had all been done BEFORE Monty's appointment, Generals Ritchie & Cunningham. Lack of success against the Afrika Korps before that had caused Churchill to 'sack' a succession of Generals... Montgomery just happened to be the one in place when the 8th Army was strong enough to get the upper hand & keep it.