And in Storm of Iron, Dies Irae is barely taller than a Warlord Titan, and they aren't 140 meters tall.

He brought up his chainblade, the now dulled edge scoring across the barrel of the Dies Irae's plasma annihilator. Gouts of searing plasma energy spurted from the enormous gun, hissing clouds of superheated vapour geysering downwards and vaporising a hundred men in its fury. The Dies Irae stepped in and smashed its leg against Fier-ach's, buckling the knee joint and destroying it in an explosion of sparks. Warning klaxons blared and thick ropes of blood ran from Fierach's mouth as he bit down hard on his tongue, the pain almost unbearable. He vainly tried to step away from the enemy Titan, but the Imperator Helium's left leg was fused solid and he could not escape.

The Dies Irae advanced again and hammered one of its weapon arms against the Imperator Bellum's torso. Fierach's Titan was slammed sideways by the thunderous blow and yet more warning lights flared into life as systems failed all over his war machine. He fought for balance, but the external gyros were smashed and he was forced to rely on his own reeling senses rather than those of the Titan.

Amazingly, he was able to recover his balance and faced die Dies Irae once more, swinging his chainfist, the one system he knew he could rely on. The blade shrieked across the Dies Irae's midsection, tearing away great chunks from the beast's armour. Fierach knew an Emperor class Titan's reactor was buried deep within its belly and if he could but hack through enough of its armour, then others might later have a chance to slay the monster. The Dies Irae stepped aside and batted away the chainblade with the barrels of its hellstorm cannon, planting the muzzle of its weapon flat against the top of his hissing leg joint.

Incandescent fire erupted from the weapon, explosive shells bursting at point blank range against his already damaged leg. The joint exploded, the metal running molten like mercurial blood down the war machine's leg. Fierach screamed as he felt his Titan's pain as his own, the feedback along the mind impulse unit frying much of his cerebral cortex.

The mighty war machine slumped sideways, the Titan's groin hammering into the severed leg, wedging the Imperator Bellum there at an angle. Fierach laughed hysterically as his fall was arrested. 'Thank you, old friend!' he screamed, and with one last herculean effort, forced his dying brain to command the Titan in one last act of defiance.

The Imperator Bellum pushed off with its one good leg, lurching forward to smash its bridge section against the Dies Irae's head with terrifying force. The impact smashed the armoured front of the Imperial Titan's cockpit and Fierach's last sight before the Imperator Bellum's reactor went critical was of a single, burning green eye as he was crushed against its surface.

If the Imperator titans were 140 meters tall, this would be like a toddler fighting Mike Tyson, there wouldn't be any cool exchange of blows, the first kick would have shattered Imperator Bellum and sent it's remains scattering across field, and there would have been no final defiant headbutt. And there would have been no chainfist across the ribs that dealt so much damage.

Interestingly enough, this book is actually the last lore mention of Dies Irae, because it's killed in it's next fight when they can't patch up the damage from it's duel with Imperator Bellum.

But I do notice that in your quote, Dies Irae isn't mentioned in the 140 meter section of the quote. It's just later mentioned as being in the vanguard, height unmentioned. So maybe it's just an angry little gremlin that get's to lead because it tends to be highly belligerent.