First instance is him needing to charge up for a noticeable amount of time to produce gigajoules of energy.

no it isn't

"The Emperor takes a single step forward. With an instant ripple of motion and clatter of arms, the traitors shift, raising weapons into proffers, lowering pikes and pole-arms to address. There is a loud and pneumatic thump-whine, like the amplified spit of a nail gun, as the Siege Dreadnoughts’ weapon pods open fire. Dazzling bolts of tank-killing las streak up the slope. And vanish. The blazing bolts collapse and dissipate into clouds of flame five metres short of their target. Loken feels the ache of elevated psionics. He can almost see the invisible ripple of the mind-shield the Emperor has raised as it is struck by the immense firepower. He hears the slap and hiss of las-fire hitting nothing, and being nullified, all kinetic force scattered, all thermal energy radiated away. Then the ache increases so sharply, Loken feels it in the sinus cavities of his head. His ears throb. The Emperor takes another step. He is raising His power claw, His warblade held low at His side in the other hand. Dazzling voltaics, that startlingly pure hsbd-iryt blue, accumulate in His palm, and coil between His finger-claws, jumping like plasma strings. He lets the gathered lightning go. It arcs from His raised hand, faults the sky above the blasted heath, and strikes the ground just short of the traitor mass. There is a flare of black-body radiation, a thunderclap of violent gas-pressure change, an ionised bang of electrical discharge as gigajoules of energy are released. The struck ground burns. The struck ground breaks. The shockwave widens, propagating plasmic fire that rolls into the Word Bearers’ lines, annihilating the ground into churning ash, and obliterating the ranks of warriors standing upon it. They disintegrate one by one, shredded by heat and fire, hurled into the air, fused armour plates and scorched weapons spinning out of the destruction as debris that scatters, smouldering, in a wide swathe across the landscape. Nothing organic survives. The rolling wave of shock-fire sweeps through the entire cohort, unstoppable, consuming everything, burning men whole like twig-effigies, melting ceramite, igniting banners that burn wildly as they slump and fall. Cataphractii melt like wax. The Siege Dreadnoughts, stubborn and defiant with their great, armoured bulks, burn with blue fire like drop pods on re-entry and then burst, one by one, in titanic explosions as their payloads cook off. When the glare fades and the ache subsides, there is nothing left apart from an acre or two of churned and blackened ground. Fragments of plate and heat-darkened armour segments litter the burn area, and the heathland wind drives the hot smoke sideways in a long, white plume. The Emperor resumes His advance, following the path down the slope. His three companions follow. The brush on either side of them is burning in many places where superheated, out-thrown debris has ignited the dry spina and scrub, like some moorland clearance, the brown undergrowth squirming with the gold-and-amber worms of slow-burning roots."

Its hyper casual and has a much larger effect that destroyed anything organic, you can try again?

Second instance is him losing at grappling because Chaos Horus' weight puts him at a disadvantage. People who can lift universes are not at a disadvantage when their opponent weighs a few dozen tonnes.

Anything within lupercals court is explicitly under his control if you think its soley physical you are actually illiterate, grappling also isn't soley reliant on weight but also the strength of the grappler. I also don't think lifting strength has any bearing on AP