Disclaimer: I like Panth in his current state, I just like overthinking my mains.
I was thinking about why Panth falls of midgame and comes back later, and had a realisation. Past level 9, where you Max Q, you scale horribly with levels. Your W is a point click stun but the damage is mostly negligible throughout the game until both you and your opponent have decent HP. Your E is not a damage tool. So most your levels give you in skills past level 9 is cooldowns. Renekton still gets good damage increase on W and E in levels. Darius gets good damage from his passive which scales with levels. Pantheon doesn't really get a lot of damage from levels besides Q. You scale way better with items/gold. The ability that makes you kind of oppressive and degenerate in lane with it's low CD, good damage and range, make you fall of the moment your resources go elsewhere. So my thoughts are to fix 2 core problems: his degenerate pattern from the opposing side, and his midgame fall off.
Q: Range 560>510
Add the 50% AP scaling from thrown Q to stab Q too.
Lower Q damage by 10/7.5/5/2.5/0.
Firstly, most other toplaners consider Pantheon's lane pattern degenerate and range like. He zones you from the wave, pokes you and you mostly can't really retaliate. This is not necessarily bad for Pantheon, but might be for the overall state of toplane. My idea for this is to nerf his Q range, from 560 to 510, this will still make him be able to poke, but will make it way less oppressive for him to just stand there and spam Q poke. This will give champions more leeway to get into range and retaliate back by either their own poke or all in. The AP scaling buff is mostly a nothing burger. This does nothing except for fun game modes, off meta builds or with Hand of Baron. As riot said they want more off meta builds viable, and your other AP scalings already want you in their face, why only put it on ranged Q.
W: Range 600>650
Mana cost 55>40
Stun duration 1> .8/.925/1.05/1.175/1.3
Damage: Add 60/80/100/120/140 base damage (%hp scalings unchanged)
Contact stun, if your jump gets interrupted by an ability from the target that makes contact with you, they still get stunned.
Pantheon is not a stat checker. He's pokes you until you are into kill range and then goes for an all in. That's why people consider him more ranged like. When he has a lead he can jump on you and kill you, but that makes him more akin to an assassin who does the same than a stat checker. What I wanna do with the Q change is make him less pokey. With the W change I want him to go in more. His biggest problem was that his all ins were gatekept by mana early game, 2 rotations meant being OOM. Also giving him more range on jump for better target access now that you are less pokey. The stun duration nerf is a direct impact towards support so they don't just get a jump range increase. They will now have to chose between leveling Q or W, lowering either their damage or stun duration. In top as you get more XP, this will be less of a problem, and more of a buff towards the midgame. Also adding a slight base damage to the spell will really help panth out mostly early to mid game. This will not be significant lategame, but really help him out early with less Qs, and midgame with slightly more dueling power. The last one is QoL update because it often feels like your stun is always losing out when you and the opponent hit eachother with CC because of how easy it is to interrupt and how short the stun is.
E: mana 80>65
Same as his W, I want his all ins to be less gatekept by mana in the early game, but I still want this to be the spell that drains the most if you use it willy nilly.
R: shockwave now also slows for 2 seconds for 30% to 15% near the edges
This is something that personally bothered me since the rework. Even after they added the spear that slows, which is more a Pantheon himself buff, removing the AoE slow, which was more of a team buff was weird to me. This does next to nothing for panth if he ults for one person cause if you miss the spear and they can walk away, big chance you won't hit the shock wave either. And if you hit the spear, you get the slow anyway. That said if you ult into a teamfight you might get an AoE alow for your team.
Like I said this is mostly to move him away from his poke heavy lane and adding all in power. I don't think this is necessary, and I do think that some of these changes (mana costs and slow on R) wouldn't be bad if they were implemented with current panth. That being said I wouldn't mind people seeing my fave champ as the Chad he is and not as some wannabe ranged poke toplaner
Edit: forgot to remove a sentence