DN not always remove. Dispel maybe can not be resisted, but this is dispel-on-hit (like Ezra) and therefore, it can be dodged - since the hit can be dodged. You see this a lot vs foresights.
After that correction, let's say - some skills say they can not be prevented, or resisted, or dodged. And that what gives them the upper hand on skills that doesn't state this specifically. Why some toons have and some doesn't? To make them stronger. Like han, as an attacker - he's amazing but not the best - and his utility of first turn give him advantage over others, and that's what the devs wanted to do.
If a toon is not strong enough, they can give him non-resistable skills to make him much better.
About luke not stunning - there's always a 15% chance to resist, after a tendown even. This chance only become 0 if the attack can not be resisted. (Han Solo shot first, thrawn fructure..)
Disclaimer about the unresistable stuff. If you are like Han (great example lol) but you try to stun zJyn, you won't be able to it. Zyn can not be stunned, so the Han stun is maybe not resistable, but just have no effect on jyn.
You can read more I'm swgoh.gg mechanics, very interesting. You'll see why Han/CLS TM removal is better than Jyn for GG in P1 HAAT, how r2 number crunch gains and gives the bonuses, and more and more.
