He was not so arrogant as to think that he alone could match a massive army.
As for his war experiences, though seemingly important, they had already been left in the "Preface Code" of the Madman's Conjectures Collection, unearthed, and thoroughly studied and analyzed by scholars, military leaders, political leaders, think tanks, and so on throughout the ages.
Thus, Harrison Clark now realized that he was not as important as he had imagined.
If the most advanced human weapons were not individual soldiers' equipment, then his presence or absence would not make much difference.
It was only a matter of days before the Compound-Eyed Observer would arrive at Proxima Centauri.
It was even possible that the Observer's fleet had already entered the Orion Arm, but was still in the state of long-distance space folding and not detected by human monitoring.