The section of Ireaneus quoted here is part of a parenthetical phrase (note the hyphens).
Some of them, moreover — [when they predicted that] as a weak and inglorious man, and as one who knew what it was to bear infirmity, Isaiah 53:3 and sitting upon the foal of an ass, Zechariah 9:9 He should come to Jerusalem; and that He should give His back to stripes, Isaiah 50:6 and His cheeks to palms [which struck Him]; and that He should be led as a sheep to the slaughter; Isaiah 53:7 and that He should have vinegar and gall given Him to drink; and that He should be forsaken by His friends and those nearest to Him; and that He should stretch forth His hands the whole day long; Isaiah 65:2 and that He should be mocked and maligned by those who looked upon Him; and that His garments should be parted, and lots cast upon His raiment; and that He should be brought down to the dust of death with all [the other] things of a like nature - prophesied
The reference is not to Jesus' weakness as a man, as though he was physically inferior to other men, but to his humility as regarding his having released his grasp upon the equality with the Father that He eternally enjoyed and His assuming the physical form and role of a human servant of the Father.
Have this mind among yourselves, which is yours in Christ Jesus, who, though he was in the form of God, did not count equality with God a thing to be grasped, but emptied himself, by taking the form of a servant, being born in the likeness of men. And being found in human form, he humbled himself by becoming obedient to the point of death, even death on a cross. - Philippians 2:5-8
Therefore the comparison is not between Jesus strength and the strength of other men but between the power of God and the physical limitations that the Son of God took upon Himself.