Why is Swain's most iconic ability so watered down?

Demonflare. AP ratios nerfed because of the fiasco that happened in the bot lane, and now he suffers because of it.

Mediocre wave clear, terrible mana management and barely able to actually have this high thematic moment that Riot set out for him during the development of his full VGU. Demonflare was meant to deliver on the fantasy that could be more than just a brainless drain-tank (which I used to 1 trick and enjoy, by the way) into a Warlock-esque champion that accomplished the idea of making Swain a Tyrannical, powerful and dark leader and general of one of the greatest nations in Runeterra.

Why did his AP ratios get knocked down so hard without any compensation? His Q feels AWFUL in the early stages of the game, and it's just not for harassing, it's his primary tool for wave clearing. Old had his old Q (RIP Beatrice) which allowed him to CS under tower and ultimately regain his mana back, as the champion before the rework was also very mana hungry, but his passive helped him manage mana.

Right now, has very little to no mana regeneration in the early game. Even with a Catalyst, your mana return is insignificant, especially into matchups where you constantly need to use Q and E to trim and manage the wave so you can SCRAPE as much Cs as you can.

Why not just give the old ultimate back if you're going to render the most impactful and interesting element of Swain's kit borderline useless UNLESS you build a after ?

Before the nerfs, Swain had infinite amounts of opportunities to turn a teamfight in his team's favor just because of the powerful zoning of demonflare. I understand the detriment of doing 1000+ to 5 people, but then again is an immobile champion who ultimately relies HEAVILY on the ability of his teammates to either CC for him or for them to follow up on his CC, however it is usually the latter at this point.

The frontline mage that a lot of old mains used to love is still there, but we only get that for 12 seconds and that isn't the problem. I mean ffs, the drain from the 12 seconds that 's ult is on for does more damage than demonflare ITSELF!

Take a look at this: https://www.youtube.com/watch?v=EmyWVRNHhuk

(Given the level difference, you still could not do this with the items I had and the current demonflare ratios)

Didn't have RoA, skipped it and went for a Morello, Liandries and Rylais build with pen boots and zhonyas. NO deathcap, high risk in the early game for being vulnerable due to lack of health and resistances, but the payoff late game is the DELIVERY OF DEMONFLARE. This build is borderline USELESS now since you lose an easy 300 damage on your ult at every stage of the game. AP ratios went from 1.35 to 1.05! And you didn't even hit the champion's reason for being strong in the bot lane. THE CC CHAIN AND SOULS. Not the ult damage. The reason why Swain was so successful in the bot lane is because the synergy between a heavy CC support and Swain's passive allows for a deadly, inescapable blow-out combo that gives Swain access to souls anytime he needs, which means the 'reward' for collecting souls is almost now just a spoon-fed part of Swain's kit. Why hit the damage on the ult? Why not increase the cooldown on Swain's passive or allow Swain to lose souls on death?

But honestly, outside of the botlane, Swain does not get souls as easily as he does with an ally support with all that delicious CC. He could possibly get a gank from his jungler, who only comes to gank when he sees an opportunity, OR.. just do it himself.

Swain is struggling right now, especially since he is a team reliant champ who is subpar at what he is meant to be, a frontline pseudo-tank battle mage when he hits R. The damage is lackluster, making the oomph behind the rework that much weaker.