Consider two employees at the same B2 level.
One is a software engineer who needs to give clearer updates and ask for help earlier. Most of that work happens with peers. A group can recreate the interruptions, follow-up questions and incomplete information of a real stand-up.
The other has just become an engineering manager and needs to prepare for a sensitive performance conversation with a direct report. Individual sessions provide privacy and allow the teacher to work closely with the manager's wording, delivery and likely responses.
Their shared CEFR level does not make their training needs identical. The format should follow the situation they need to handle.
The
CIPD guidance on learning methods recommends choosing delivery methods in relation to the learning need, organisational context and practical constraints. That principle is useful here. Group and individual lessons are delivery choices, not programme goals.