Why have "ozone-depleting substances" led to a third of all global warming and half of arctic sea ice loss?
The Global warming potential (GWP) describes how much global warming a particular gas may induce in a particular time period.  It is often expressed in terms of CO₂-equivalent.  The best known greenhouse gases are carbon dioxide (CO₂), methane (CH₄), and water vapour (H₂O).  Water vapour is short lived and therefore its emission is not a primary climate change contributor (but it is a strong secondary contributor through the water vapour feedback).  However, there are other greenhouse gases that are, per unit volume, extremely strong.  Some of those are CFCs and HFCs.

Wikipedia quotes various IPCC reports and summarises the 20-year global warming potential of some greenhouse gases (emphasis mine):


CO₂: 1 (by definition)
Methane: 86
Nitrous oxide (N₂O): 268
HFC-134a: 3790
CFC-11: 7020


The GWP is a result of a combination of the strength of radiative forcing and atmospheric lifetime.  The radiative forcing is about 20,000 times stronger, due to those complicated molecules having lots of rotational and vibrational states that can absorb IR radiation.  Fortunately, their lifetime is also shorter, resulting in an estimated GWP of around 7000-11000 for commonly used CFCs.

So to answer your first question: yes, ozone-depleting CFCs have a very strong greenhouse gas potential independent of their ozone-depleting properties.  Their replacement, HCFCs, are much more gentle to ozone but still very strong greenhouse gases.

I'm not sure why their effect is relatively stronger in the Arctic.  The research article you linked provides some ideas:


  It is also legitimate to ask whether such a large contribution of ODS to Arctic warming might be an artefact of the CAM5LE model.
  (...)
  In addition to a larger RF, two factors produce an enhanced Arctic warming with increasing ODS in CAM5LE: (1) a stronger lapse rate feedback (which is positive for the Arctic, confirming previous work) and (2) a weaker negative net cloud feedback (with contributions from both long and short waves).




Note that the article seems to entirely ignore that HFCs are not phased out at all — HFCs have largely replaces CFCs because they don't destroy ozone, but still have a strong GWP.  I find that a rather serious omission because it strongly undermines their conclusion that the phase-out of ODS, which is well under way, will substantially mitigate Arctic warming (the article groups HFCs together with CFCs, which makes sense for GWP but not for ozone depletion).