I would agree with your interpretation - I'd be interested to hear if anyone else had a differing opinion? Just note that the wording of FCL.915.FI was updated recently and it now says:
(2) hold at least a PPL(A) and have:
(i) except for an FI(A) providing training for the LAPL(A) only, passed the CPL
theoretical knowledge examination, which may be taken without completing a CPL
theoretical knowledge training course and which shall not be valid for the issue of
a CPL; and
(ii) completed at least 200 hours of flight time on aeroplanes or TMGs, of which 150
hours as PIC;
It makes no difference to your query, but it will allow you to self-study for the exams. If this is the case, they won't be subsequently accepted for a CPL.
Is there a place you plan to instruct after you get your FI? If so, you should ask them if they offer the LAPL licence. If they did you can instruct for that without CPL knowledge. 98+% of General Aviation aircraft in Ireland can be flown on a LAPL. I really don't know why most people are still training for a PPL. I would invest your money (and time now) in getting a good quality instructor rating as this will stand to you more than doing CPL exams to meet the requirements of instructing for a PPL. If you subsequently did the CPL exams, you could then instruct for PPL.