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Benny89 I don't think you understand the math or theory behind most the default optimization suggestions.
A paladin self-casting haste on himself is vastly overrated.
A paladin using GWM is vastly overrated.
The biggest reasons are
#1 Damage Now vs Damage Later
#2 GWM's -5/+10 benefit is only really good when accuracy can be fixed some way. Paladins lack a non-action dependent universal accuracy fix. They do have bless but refer to #1 for why that isn't really a great idea. Vengance Paladins have their channel divinity but that only works on a single enemy once per short rest. PAM is more universally applicable and for many enemies it has a similar impact to GWM.
EDIT: I stand corrected about Bless. My apologize for my mistake.
However it still doesn't change my mind that Damage Later is better if you have harder encounters and they don't end in 1-2 turns.
Rule of Thumb: the more turns fight last- the more GWM will outperform non-GWM PAM build on Paladin.
Yes it is Damage Now vs Damage Later but if you have enough higher Damage and your fights are no 1-turn ez-mode fights (if they are there is no point in optimization anyway) that higher damage will overperform lower damage the more turns you fight. Losing ONE bonus action, ONE bonus attack for having much higher DPR and Nova in next turns is very fair trade-off.
As for Channel Dinivity and Haste - you use that on Boss/Big Threat anyway so you said nothing new. Who waste VoE on something else? Haste + VoE again will overperform lower damage in next turn vs non-Haste non-GWM build.
I also showed you that we could easly NOT cast Haste on Boss fight and we would still outdamage non-GWM PAM even with 1 less attack.
I speak from experience playing tier 3 as Vengeance Paladin.
It's also a matter of your DM. If your DM throws at you Bosses that can be killed in 1 turn from just smites alone or encounters during day that can be end in 2 turns- then I tell you this: there is no point in optimizing builds anyway because everything will die anyway.
When I had 4th level as Vengeance Paladin I had one-on-one duel with CR9 Assassin and I killed that assassin in 4 or 5 turns. I had 2 HP left, used all my full Lay Down Hands and lived because I got good save throw vs Poison. Without GWM He would kill me because even will burning all Smites - it was barely enough damage. And those are the types of encounters my party face.
Also if you say Haste is overrated - your fights are not challanging enough. I can't imaginge fighting vs Bosses I face in at my table without extra AC, speed, action and attack and advantage on DEX saves (STR Paladin have poor DEX saves) because I literrally have to use all of that to beat encounter most of the time. My DM doesn't care about default CRs in DnD (adn that is good, because players scale way faster than monsters) and give us much higher CRs than we should be facing and that is where higher damage comes on top and losing 1 turn for setup/casting etc. is more beneficial. Also you seem to have mind set of fights as some sort of fights in cage where opponents (monster and players) goes in, referee says fight starts, they roll initiative and only then they can start fight. Unless it's an ambush situation - you can pre-cast Haste in 8/10 times before fight starts, at least that is my experience. Unless all your encounters are "suddenlly a wild encounter has appeared! You have to defend yourself" which is not my experience from playing RPGs.
Now this is why I prefer Damage Later vs Damage Now as in my games- fights don't end in 2 turns. Unless at your table your typical "Boss" when you are level 20 have less than 300 HP (then I don't know why to even care about optimizing...) and you can nuke it in first turn with just PAM + Smites.. However if that boss have 700HP you will fight it for probably more (considering more stuff going around) than 2 turns which is where GWM will come on top. 3 turns you will be a lot of dmg behind GWM build.
GWM will also vastly outperform non-GWM PAM build in fights vs hordes as usually hordes are low AC low HP enemies. GWM will allow for much faster clear up vs those too and as we know- hordes are issue for Paladins due to lack of AOE options. However being able to kill 1 enemy in horde in 1 or 2 attacks and killing 2-3 enemies per turn vs killing 1 per turn is a big benefit for Paladin.
It's like playing Bladurs Gate 2 solo at Easy mode vs playing it at Insane. On Easy mode you can just go in with armor and slash enemies and don't care. Build doesn't matter. On Insane however you will spend your first turn or even few to cast defensive spells etc. because otherwise you will be dead. This is not wasted turn- this is needed as longer you fight- you get more benefits from extra steps you have taken. Casting Haste + VoE in first turn to be able to oblitarate enemies in next turn more easly is not a big loss. And if you are able to pre-cast Haste before fight- it's then a pure advantange. It's roleplay game, not cRPG simulator.