Gasax
Straight in in the way you describe can cause a conflict but with modern aircraft equipt with GPS it is quite usual to call at six miles three miles and finals.
If someone is on base ahead ok on a left circuit break right onto the dead side and fly a normal pattern but at circuit height.
Conflicts are not just with aircraft on straight in approaches but can happen downwind with aircraft on different width of downwind and differing speeds and at any time in the OHJ.
Obviously you would not take a straight in on a busy day and always with communication with other aircraft its not the circuit I have a problem with but the OHJ!
Non radio aircraft are a rareity nowadays and that itself is an arguemnt for updating the status of a standard overhead join to just one method of joining.
The standard overhead was created in just those times when aircraft were non radio.
Pace