Realistic battles seems better, more realistic to medieval mob fighting ... but it's not formation fighting.
We need both, realistic mob fighting and realistic formation fighting, depending on unit training. For example, Greek hoplites would only fight in a phalanx where as their opponents gaulish warriors would only fight in mob.
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This is true for neither hoplites or gallic warriors.
Hoplites fought in a semi coherent mob until the hellenistic period and the transition to long pikes (best exemplified by the macedonians).
Gauls.... fought in a semi coherent mob because forming a shield wall is intuitive and effective. Indeed, it is possible the gauls fought in more coherent formations. Certainly celtic migrations through greece saw some success in conflict with the distinctly superior to classical hoplites hellenistic armies.