|Figure 1: A creature with a morale score of '7' has an almost 60% chance of failing a morale check compared to AD&D's base morale of 50%.|
Since D&D Morale rules mandate the use of 2d6 instead of d% as in AD&D, comparing the two systems requires looking at the distribution of outcomes. If a relatively cowardly monster in D&D has a morale score of 7 then I would argue that the weakest D&D monsters are slightly less aggressive than in AD&D where their base morale score is 50%. That's assuming the morale rules are applied under similar circumstances and left unmodified. The modifiers are where things get complicated, though.