Depends which variant. T Davies Daleks would be an arc ender, on the scale of the Annihilation Wave. Everything you thought they were weak at was merely something to give you false hope, before they exterminate you.
Moffat's Daleks are all hopeless, bar the one Big Boss Dalek who turned against them all, and spends his days sniping Skaro citizens for fun. Every sliver of hope they get is crushed in another wave of Matt Smith's smug prick face.
Chibnall's not bringing back the Daleks, which is mildly surprising, because he's shown he's not above doing literally anything Davies did but less subtlely. How the actors in Doctor Who don't murder the writing staff I haven't the foggiest.
Old who? They'd be a threat, but it's really hard to tell, because there wasn't exactly a consistent power level, even for Doctor Who. Honestly, the old Time Lord skeletons in the closet would be a bigger threat, mainly because they're willing to wipe out physical existance in favour of psychic energy.