The same is probably true of IR holders who don't work in a job which requires it regularly.
Maybe, but that is not my experience.
I fly a great deal with people with PPL/IRs (both FAA and JAA/CAA), none of whom are professional line flyers (some have ATPs and CPLs, but they don't use them) and I have only seen a high level of capability and professionalism.
That is not to say that that there are no gash PPL/IRs, far from it, but I have to say that the standard I see is very high.
I think that that is because most PPL/IRs make almost every flight under IFR, right through to an IAP, even when VMC, whereas most IMCR holders don't.