Going with this idea (and bearing in mind it’s like 1am here and I’m hopped up on muscle relaxers and hydrocodone . . . ), then before the wars Rajaat would have been insanely powerful. But truly honestly recreating the Blue Age would have involved a level of rewriting reality that would have been beyond his power.
So the plan is this: sacrifice untold millions of lives and harvest the energy. Use that energy to LITERALLY recreate the Blue Age and all that entails. This is a plan that will take centuries and millennia. Channel the power into the Pristine Tower, accessible from the Dark Lens.
To make the plan work, you’ll need collection units. These are the champions. As part of their nature, they passively absorb the death energy around them. Let’s take the explanation of templars that the champions could empower followers once Rajaat made them champions. Templars, also, will passively absorb death energy, channeling it into the PT.
Manufacture the cleansing wars for the sole purpose of creating an apparatus of death, to stockpile over millennia the energy needed for Rajaat to become godlike enough to rewrite reality to his whim.
The champions rebel, trapping rajaat. It works because of the surprise, taking him out when he didn’t have access to the dark lens and the vast stores of power.
Even with Rajaat imprisoned, the champions are STILL passively empowering the tower. For 2,000 years. Especially with Borys bringing the planet to the verge of death, that’s a LOT of empowerment.
Tithian frees Rajaat with the dark lens. Immediately, Rajaat has access to this untold energy. Although making him essentially omnipotent and he easily curb stomps the champions, he’s still acclimating to the new him, and his reality revisions (like the newly blue sun) are still tenuous. This also results in him getting blindsided by baby Rkard, which mostly reverts his revisions.
In making this ritual and linking it to the PT, Rajaat made use of a pre-existing network of life energy on the planet (ley lines). With the flood of death energy overwhelming this network, bordering planes became corrupted, creating the Gray, which unnaturally prevents all souls from leaving Athas, which in turn funnels the energy of those souls as they dissipate, right back into the PT.
Indeed, considering the probably nature of the PT (an artifact intended to access/funnel energy, most notably from the sun), you could even say that the massed energy from the wars was funneled into a pocket demiplane created for that purpose, and the tower/lens were merely conduits for Rajaat to access/direct the energy stored therein. That plane could either be the gray directly (making its creation by rajaat purposeful, even without understanding the planar ramifications thereof), or another plane like the Black, or really just a random demiplane made for that purpose.
It’s important to note that Rajaat was NOT an expert on planar travel and clearly had a very rudimentary grasp or even gross misconceptions about it. Per the experiments in the future Dead Lands. However, Nibenay/Gallard at least knew enough about the subject to discover the Hollow, so it’s possible Rajaat could also have discovered a suitable extraplanar means to store the energy for his ritual.
Hell, the pocket plane to store all of that energy could have BEEN the Hollow. Imagine the irony there: Gallard traps Rajaat in a reality of nothingness he discovered. Except it wasn’t nothingness: it was a storage device/plane for enough energy to rewrite reality, made to keep said energy in an inert state. And they dumped Rajaat there for two thousand years, with a constant influx of additional energy.