Before Bosey/IO540 jumps in, the downside to any of these is lack of IMC/Night on a Permit aircraft, but you could always rent a spamcan for such activities if you were so inclined.
There is no real argument here - it comes down to what mission capability you want.
If you are happy to stick to local flights in nice weather then VFR is OK. (But you better not be an owner because you are likely to soon get fed up with going nowhere). You can "go places" VFR but only if you are retired and have loads of time
If you are yourself instrument competent (not necessarily instrument legal) and you have a suitably IFR equipped plane, then you can fly "VFR" all over Europe, in cloud as necessary, and so long as you make sure the arrival is always obviously VFR, and there are no incidents, then you will always get away with it. Unfortunately very few pilots with no IFR background will be able to pull this stunt off consistently because it needs IFR planning and IFR weather understanding...
If you need the capability to fly IFR, landing with an instrument approach, then you have to do it legally, and unfortunately one needs a CofA plane for that (in the UK). It's a revenue maintenance measure by the CAA, no more; if they allowed IFR in Permit types or if they allowed common spamcans to go on Permit then a chunk of CAA income stream would vanish. That's why EASA is being slagged off everywhere right now for its latest pan-European proposals. They are too much "fresh air".
BTW I don't think you can just "rent a spamcan" for the occassional IFR flight. For a start, you won't be IFR current, and you won't be current on the type (very important for IFR). If you rent a C172/PA28 once a year for some rare flight in IMC, you are going to get yourself killed. But you also cannot generally rent a spamcan that is any good for real IFR, due to poor condition or poor equipment (there are exceptions). And renting is not feasible if you want to go away for days or more, as is typically the case if doing a longer flight out of the UK; part- or whole ownership is the only way to do that.