I don't think it has better dialogue just due to the fact that the quality of writing in TW3 is flat out better, but I can see why you think this even if I don't agree.(you prefer the political tone) The Witcher 2 does have great replay value, but I'm not sure it's actually better than TW3 in this regard. There are way more different outcomes to see in a replay of the TW3 than TW2 even with TW2's branching Act 2&3. It's just a bit easier to replay TW2 since it's the shorter game.
World design, exploration, atmosphere, soundtrack, monster design and side quests are far superior in TW3. Gwent is so much better than arm wrestling and dice poker. Linearity isn't necessarily a bad thing, but I just find the game to be entirely too restrictive in comparison to TW1 and TW3.
Political world building is better, but that was the focus of TW2 so it really should be. I like the combat a lot more in TW3 than the TW2. To me, TW2's combat is barely serviceable and that's only with the rebalanced combat mod. Quest design is highly subjective, but I feel the best quests in TW3 are better designed than the best in TW2. There were more meaningful choices to make in TW3 overall as well imo. TW3 also has better characters, but obviously TW2 is no slouch in that area either. The main story itself is probably slightly better than TW3 just due to how focused it is, but TW3's resonated with me more because of the cast.