One more question ... how long has this course been running? Does 'client' forsee a day when this course will no longer be required? When? 2030, 2040, 2050?
Is the expectation of 'client', that this 'forever course' should never loose users accounts, would always be able to view ALL data on ALL users? If so, you'd better check other settings site wide - 'life' of a user account even if in-active for years ... as an example - other settings ... events/tracking/completions etc.
This is not really a question for discussion/justifications ... just a thought ... Uhhh ... site such as that will only grow ... and one doesn't have 'unlimited' space, nor processing power, nor unlimited x y z.
'SoS', Ken