How do these raiders compare in strength to the ones from the starter
Do you mean the starter set or the Raider core box?
Sorry the raider core? Is the ack pack more powerful versions of raiders or are they there for role playing reasons
Ack-Ack, Sinjin and Avery are unique characters who have different attributes and skills.
Ack-Ack is a bit more powerful at ranged combat than the Raider Veteran in the core box and has some very useful skills, but she’s less proficient at melee.
Avery is a real sniper, basically the most accurate shot of all raiders.
Sinjin is also a good shot, but can only use handguns. He has some decent situational skills and can use luck without being made heroic which is nice. He’s also very sturdy.
However more important than how powerful they individually are, is the compisition of your warband. I’d recommend you to check out the PDF file for the unit cards. There you can see for yourself how good/bad Ack-Ack und co. are.