(a) conform to the pattern of traffic formed by other aircraft intending to land at that aerodrome or keep clear of the airspace in which the pattern is formed
I think it has long been accepted by most people as implicit in this statement that the onus is on traffic joining the circuit to make adjustments to their track and speed to 'fit in' with traffic already established in the circuit pattern, whatever size, or shape of circuit the established traffic is makiing, and that, once established in the circuit, each aircraft must follow the one ahead.
The problem is: When does the 'joining' aircraft become part of the 'established' circuit traffic?.
In my opinion, an aircraft joining the circuit straight in, from a 'long final' position is not part of the circuit pattern until it is inside whatever 'base leg' any already established aircraft is flying at that time.
This means that any such aircraft coming into conflict with any aircraft on the 'base leg' must, by definition, be still 'joining', and not yet 'part of' the established circuit traffic. It must therefore, make an adjustment to allow the aircraft established on 'base leg' to continue unhindered, and the only safe way to do this at this point, is to 'go around'.
As to the 'Always be witiin gliding distance of the runway whilst in the circuit' argument;
It must be appreciated, and accepted, that
any form of 'powered approach' must, by definition, leave the aircraft, at some point, and for the remainder of the circuit, unable to make it to the runway in the case of an engine failure .
The only way to avoid this situation, whilst at the same time maintaining the order of traffic in the circuit, would be for everyone to make glide approaches from the 'downwind' position, in the style of WW2 Tiger Moth practice.
I would suggest that, considering the wide range of aircraft we have in circuit patterns today, and the general unwillingness amongst many people to conform with the conventions we already have, this would be impossible to achieve.
MJ
