But, I think it is ironic that several of these items either cannot be mitigated at all without a buddy, or mitigated only with difficulty, and possibly not effectively:
Cramp (potentially difficult to mitigate)
Entangled (potentially difficult to mitigate)
Lost (more difficult to mitigate--a buddy also navigating can eliminate)
Bubble checks (impossible)
Medical emergency (impossible)
Disoriented (impossible if medical, otherwise a sign of incipient panic and a buddy can help greatly).
So, this list is as much an advertisement for buddy diving as it is a manifesto for solo diving.
The other items--yes, solo training and proper gear can make a buddy unnecessary for these.
But, bottom line, you are more at risk solo diving. This should always be clearly understood.
But, I most definitely agree that people who are equipped and properly trained should be not be barred from solo diving. Showing "the card" might be the only to demonstrate to an operator that you are, if you depend on operators to reach your dive sites.
Lets go through your listed points:-
Cramp - if you cant deal with a cramp yourself whilst diving (basic OW) - you were not paying attention
Entanglement - the entangled diver should be the one to deal with the entanglement, with support from a buddy if at all needed, as there is a risk that both divers could become entangled. also the right equipment for dealing with entanglements. ie line cutters and shears, not the 8" dive knife used to fend of sharks.
Lost - if you get lost on a dive you should first
STOP, assess the situation and if it cannot be resolved end the dive = no dive buddy needed here then.
Bubble checks - do we have to wait to get in the water to check for leaks, no of course not an environmentally friendly soap solution can be used pre-dive to check for leaks = no buddy needed here then. Constant correct monitoring of your SPG whilst diving would indicate a leak should it happen during a dive, with the use of feathering of the cylinder valve if required to end the dive and return to the surface = no buddy needed here
Medical emergency's - not sure what a buddy could do underwater, other than inflate your bc, you cannot give CPR whilst underwater or at the surface until your back on the boat or land, other physiological signs narcosis ect... ect... the diver should be aware of the basics and what to do to reduce the risks before he enters the water = so buddy required yes and no
Disorientation - see lost
all the above are to do with diver training, and nothing to do with the supposed heightened risk of solo diving.