I think you are getting confused over the nature of an Isobar. Forget wind and geostrophic forces - an Isobar is merely a line of equal pressure. It can be almost any contour it wishes!
Yes, wind flows from high to low pressure, so it 'tends' to flow from one isobar to the next, but is 'deflected' by GF. GF itself has nothing to do with wind. It is an apparent force which acts on any moving particle, be it a cricket ball or a lump of air, and is the result of the earth's rotation.. Whenever that particle moves, depending on its latitude, of course, GF will appear to deflect it to the side (being careful here 'cos of your 'origin'
). Forget acting "parallel to straight isobars" - that is the definition of a
pure Geostrophic Wind. Consider it to act at 90 deg to the particle motion and in practical terms tangentially to the curved isobars, except, of course, other effects such as centripetal (oh, ok, centrifugal) forces modify the wind from the theoretical to that experienced in curved isobaric systems.
The answer to your final question is, as 'streety' says, never in
real terms due to orographic and other disturbances but sometimes pretty close, and often between two 'matched' pressure systems as per the pic.