I'm wanting to go full Weapon Finesse for Aldari Defender, and while Dueling Sword seems the class-made way to go I've heard that there are a whole bunch of really nice Rapiers in game.

If I didn't go for DS would I be seriously gimping myself?

well fist of all I'd say you will be gimping yourself going dex with aldori. class has literally nothing that rewards dex. not saying you can't do it - saying you will have to work hard to get the same results pure class str aldori gets for for free.

Dex Aldori for build pointers if you want to do it.

and yes things like defensive parry require you to go aldori sword. that's a lot of AC.

IMHO th only reason to not take Duelling sword is if you want to dual. Aldori fencing mastery is a good Feat

WPN focus/finesse/duelling mastery/slashing grace ab+7 dam 6-12 21AC at second level without min/maxing

no it's not. it is worse than shield spell any alchemist can cast on you through infusion. or you can cast on yourself with a scroll/wand. the other part of the feat you get through slashing grace,

pooh

All those things work 'With" aldori mastery, You can secceed in the game without Min/Maxing and rules exploits.
Your way is fine for those that want it but it is far from the only way,

What I sauid above plus the cleave chain /specialization chain and crit buffs and I might not even multi. or I might if that's what makes it "Fun" for me. like bard or Pally. but not just to get their special abilities.

I have avoided getting into this with you because I Don't want to fight and flame but every time I make a comment you shove your "opinion" up my nose. and they are just that opinions.

bonuses from the same source do no stack. both give shield bonus. should not stack. will test to be sure.
upd. yep. I am correct. shield spell and Aldori Dueling Mastery do not stack. them not stacking is not an opinion. it's a fact. and I don't say something like "don't do sub-optimal things" - play whatever you like. I just objected to calling feat the effectively gives you +2 initiative "good"

I am sorry if I somehow offended you. I will try to not reply to your posts in the future.

I disagree with characterizing Aldori Dueling Mastery as just "+2 Initiative". The Shield spell has a target of Personal, so only the duelist can cast it on themselves. And while some Sword Saint levels aren't uncommon in these builds, if you don't have the ability to cast it, then the +2 shield AC is great. And even if you do have some Sword Saint levels, you'd be better off with a number of different spells than wasting the time to cast something that effectively only boosts your AC 2 points.

alchemist with infusion can give personal spells to others. wands of shield are common. scrolls are really cpmmon. also 2 points of AC is a lot. people spend 2 feats to get 2 points of AC. and AC is all or nothing in this game. medium-ranged AC just doesn't work and is a wasted effort. if you are stacking - you have to have every bit you can get. if not - don't bother with AC at all.

Forcing an Alchemist into your party is an even bigger obligation than dropping levels into spellcasting classes, and again, wasting time to buff before every single fight for a mere +2 difference in Shield AC is just plain terrible. And my unarmored duelist has an AC in the 50's without using shield spells or any other spellcasting buffs. Anything likely to hit AC 55 would probably hit AC 57 too.

Time wasted casting Shield, Mage Armor, Barkskin, etc. = No.
Time utilized casting Mirror Image, Blur, Displacement, etc. = Yes.

considering Alchemist is the most broken thing in the game it's not exactly a drawback to have him in the party. and it's not like you buff in combat. and proper duelist with buffs is in the 70's on AC. not to mention you do have to spend a feat that could be used elsewhere. getting dex builds rolling is not exactly relaxed on feats.

what I am saying is that on challenging and below it doesn't matter - you will be fine. on hard and up optimizations are welcome. and again 2 AC is actually a lot. most feats give one. most classes that do ramp AC bring +1 every 3 levels. so it's like being 6 levels behind in terms of AC progression to put it into perspective.