my second issue with base joins is they occur at a time when the pilot (or low-hour, possibly solo student) is very pre-occupied with power/flap/configuration settings, not to mention the pitch/roll changes that cause momentary blind-spots
This brings up the question of the quality of the assessment used to determine the competency of the pilot to be flying solo in a busy circuit. Unless the pilot has been certified competent to operate in the circuit
and not be "very pre-occupied with power/flap/ configuration changes, not to mention pitch/roll changes that cause momentary blind-spots" his instructor is reckless to authorise the pilot concerned for the solo flight.