What will be of the "Less" classes?

huh???

Lets say u got a 500 stat sin

1 is dexless with 500 luk and the other with 400 luk and 100 dex

with the potential items 500 luk sin will get 500 luk * 10%luk while 400 luk sin gets 400 luk + 10% luk...now you tell me which 1 is stronger

Well, let's do the calculation, shall we?

Let's figure that a Dexless sin will be using a 51 ATK Kandayo (+18 ATK from base), 10 ATK WG, 12 ATK pot, and Ilbies - a very likely scenario. This gives you 100 ATK.
To keep things the same, let's assume a Red Craven with the same boost to weapon attack that the Kandayo got (+18) bringing the total attack to 65 ATK, 10 ATK WG, 12 ATK pot, and Ilbies. This brings the total to 114.

Dexless Sin:
2.00 * (4 * (500 + 50) + 25) * (100 / 100) = 4450
All sins must have 25 base DEX, so that's why 25 is there.

Regular Dex:
You said the regular dex sin would have 100 DEX, which is really +75 off of the base 25. So I will take 75 from LUK and put that into DEX for a total of 425 LUK and 100 DEX
2.00 * (4 * (425 + 42) + 100) * (114 / 100) = 4487

Dex sins have just as good damage as dexless sins. Perhaps even better, though, because higher level items grant better potential system bonuses. So, in the end, DEX sins make a hell of a lot more sense than dexless.

For example, level 100 items which the DEX sin can wear can give +9% +9% +9% on LUK which gives +27%. The Kandayo can only give +6% +6% +6% = 18%. Which would you rather have?