Yes paladin is getting a nerf granted, but it's a nerf across the board so I think it's more fair to look at this relative to other classes taking advantage of crit-range expanding abilities being doubled by IC. I'll address each of your points here.
1. "First he lost a critical threat range on both weapons for a total of +2 loss."
Let's just be clear here, it's a +1 from each weapon due to HS expanded range not being multiplied by 2. That's not the same as a +2 loss. This is due to the change to IC; relative to other classes, paladins are not losing anything extra on the critical threat range expansion from HS (nothing is multiplied by the IC feat anymore with this upcoming update).
2. "holy sword only works on the main hand weapon when rangers can have their own version of holy sword"
Holy sword only working on the main hand is indeed a nerf directed at HS and paladin specifically and I agree that it's probably a little excessive. However, I'd be careful not to confuse this with ranger having their own version of HS. HS costs nothing more than 14 levels of Paladin to obtain; on the other hand, Ranger version of HS as you put it requires 12 Ranger levels but also 42 AP investment to obtain the level-12 cores in 2 enhancement trees. It's a lot more costly for Rangers to get their HS in this regard and also keep in mind that rangers don't have the option to take multiclass and spend 42 AP in other trees if they are to insist on obtaining their version of HS
3. "the critical threat range effect from exalted smite was also reduced by +2 for not doubling with improved critical".
I'm fairly certain that Exalted Smite's threat range was never doubled by Improved Critical; it was always a straight +2. Anyone feel free to correct me if I'm wrong here, but as a long time paladin player I'm pretty confident this is the case. There is no additional nerf to Exalted Smite beyond the Improved Critical change that indirectly nerfs Exalted Smite through not multiplying a +1 crit-threat increase from HS and other crit-range expanding abilities. Again this is the same nerf that affects all classes using crit-range expanding abilities.
4. "twf feats not providing melee power anymore"
While not a paladin specific change, I would wait to see how this balances out with the faster attack animation on the TWF chain's 4th attack. Testing will have to be done to update Vanshilar's attack speed index which currently puts TWF at 102.2 swing animations per minute with a 15% attack speed boost such as you would find from Haste spell or Speed XV enchantment found on epic level items. Depending on the results, the overall outcome could be a nerf, a buff, or neither. (Link to Vanshilar's work for your reference:
https://www.ddo.com/forums/showthrea...x-and-Formulae)
Finally, the comparison between ranger and paladin at the end of your post could also be made without the balance change since rangers and paladins didn't get any extra nerfs or changes other than HS not applying to the offhand. (Ranger have these abilities in their coes already and they are not to be changed directly with the upcoming Balance Change).
It hardly seems fair to compare Ranger's 2 tier 4 cores, 1 tier 5 core, and 1 capstone against 1 spell offered by level 14 Paladin. I would think the difference would be greatly deflated if you made a fair and more comprehensive comparison with the respective Paladin cores.
(While we're on this topic however, I noticed you highlight 10 melee power from the ranger capstone which seems like a striking difference between the two classes at first until you see that the KotC capstone offers 10 melee power as well as part of it's effects. Also 10% extra offhand strikes is not the same as additional double strike. The actual difference in double strike should be 5% from Whirlwind and 25% offhand doublestrike from Dervish. (For the sake of simplicity we'll say DS = offhand DS).
You are also omitting Zeal as a paladin exclusive buff to double strike, bringing the difference down to 20%.
If you were to translate this into raw % difference in DPS solely based on the amount of double strike, then you need to take into account other sources of double strike as well. A twf player would reasonably have ~10% enhancement bonus from items/DC destiny's Celestial Champion, Perfect TWF feat with 5% double strike and 10% offhand double strike. That's 25% double strike as a baseline. Take 145% over 125% that's only a 16% difference in overall DPS, significantly lower than 40%. Add in Martial Epic Destiny Past Life Doublestrike Stance (9%), that difference becomes less than 15% difference in terms of calculating raw % DPS difference from double strike alone. And that's not taking into account if you were to do a equal comparison by adding the respective paladin cores.)
On PRR and MRR: I don't think they are nerfing HS because of the PRR and MRR in SD. That's not the message I got from the devs here. They claim to nerf HS because it was overperforming in terms of TWF and it's interaction with IC feat (their claim, not mine). On a separate note, their concern with SD's 25 PRR/MRR isn't that paladins could get it but rather that it was relatively easy to obtain with a 3 paladin splash and just 6 AP. (Again, their reasoning.) Indeed you recognize this when you say that rangers can get something equivalent through their capstone which requires a 41 AP investment and inhibits any multiclassing.
All in all, I think you would be much happier if you took a more comprehensive and fairer comparison. I don't believe it's as bad as you believe it to be in your post. My estimate is that TWF Paladins will still be an extremely viable and strong build should the current balance changes go through to live. These nerfs are for the most part across the board so relatively speaking it doesn't make paladins so much weaker vs other classes so much that it makes everyone affected weaker vs mobs in general. I'm in the same boat as you playing a long time TWF paladin myself. =)
Hope that helps!~