So what is the real reason for this thread? Of course you don't have to have completed your ATPL's before CPL. If you only want a CPL why would you even need to sit ATPL's?
As for the ground schools, quite often students can have passed their IR without completing the ATPL's as they are waiting on re-sit results. The schools don't recommend this situation but it is allowed. There appears to be no foundation to your point at all.