That's not exactly Lysandre's motive, though I don't blame you for not catching it. He gives his motives why he's doing things in chunks and they're very much "blink and you'll miss it" moments. Lysandre is also a more dramatic person so he bury his motives in somewhat fancy talk and a few time metaphors. To put Lysandre's motives simply:
- Lysandre is a descendent of a king of Kalos (revealed to be AZ's younger brother who took over ruling after AZ banished himself after firing the Ultimate Weapon & Floette abandoned him), and though he is not royalty as Kalos doesn't look to have kept their monarchs, he still feels that he has a responsibility to help the people of Kalos.
- I'm guessing before Lysandre's company Kalos had a problem with a lot of people living under the poverty line as Lysandre's focus of helping the people was to improve everyone's lives. He did so by going to university/college to learn about technology (this is likely where he met Sycamore who was one of his teachers) and after so started his company.
- Lysandre's goals were noble and he helped a lot of people and uplifted Kalos's reputation. However, Lysandre fell into a mental sinkhole of thinking he needed to help EVERYONE and despite all the money and time he spends there are people who he still can't reach out to help. This began a spiral of madness for Lysandre, figuring out why he couldn't, and he came to the conclusion is that there simply wasn't enough resources for everyone. And not just in Kalos, the entire world he viewed having an overpopulation problem. And this caused suffering, notably for the poorer people while the rich not only took what they needed but also greedily hoarded and held onto more resources that others could use (money, land, opportunities, media attention, etc.). If things kept going as it was now he concluded the world would be consumed away and in the end people will be fighting over the few resources that are left until there was no more.
- Eventually Lysandre mind broke. He could no longer see past most people being selfish, greedy, and uncaring for each other and the world. He decided, since he's the only one who cares, he'll remake the world in his own image and only for those who believe what he believes. Thus he started Team Flare and came up with plans to use the Ultimate Weapon he likely knew about as it was a secret kept with his family throughout the ages. He knew what he could do so planned to make himself and all his followers immortal while then wiping out everyone else (each game only explained one side of his plans to match the game's Legendary though it's clear both goals were intended to happen thanks to AZ's story explaining the Ultimate Weapon's dual power).
So he's not trying to destroy the world exactly, plus his thinking is kind of messed up because he's essentially insane/mentally unstable but is good at hiding it. You and I know that Lysandre's plans will of course not work, but that's not how Lysandre sees it. Heck, we already see his plan is hypocritical because, even though he started with the goal to help the poor people and saw the rich as greedy & responsible for this, to even join Team Flare and survive into the new world you need to donate 1 million Pokedollars to Lysandre! Poor people can barely afford food and rent for the month so how are they supposed to donate a million dollars, and for rich people a million dollars is a drop in the bucket! It's why I'm interested in learning the waiter & waitresses in Lysandre's cafe were actually still paying off their Flare due; are there other Flare members like this who couldn't pay the one million but were still allowed in as part of a paying program? That would at least somewhat make Lysandre less of a hypocrite, but then again 1 million is still A LOT and are these people still expected to pay these dues after Lysandre wipes the world clean thus money has no relevance without a world population to give it value? Also, isn't Lysandre's company rich? Why does he need a million from each member when he likely already has the money and technology to unearth and upgrade the Ultimate Weapon? I can only see it as being some kind of "loyalty test", you're literally paying all you have to save your life, but once again that thought would only work for maybe middle class citizens and even they probably don't have that much, MAYBE if you're a small business owner, in a comfy position as a higher up in a company, or are old enough to save that much/inherited it. That million dollar entry fee never made sense to me, it's one of the few things which is holding back Team Flare & Lysandre from being an interesting villain team so it doesn't match-up with their goals.