My biggest question is, if you need to move the catapult to the fantail because of the trunked funnel, why bother with the trunked funnel in the first place? The whole point is to free up deck space, not sacrifice it.

I don't know why you want to move the catapult to the deck, there's a reason why most navies had them amidships. USN practice kicked it to the fantail because of a lack of priority for it, in part because not only did we have carriers fairly early on, but some pretty large ones (other than escort carriers and the Independence/Saipan class emergency programs we never had a carrier smaller than Langley and Ranger). The whole point of trunked funnels is that you can consolidate the superstructure for a better protection scheme and/or firing arcs - in fact, on that note, you can rearrange the superstructure on HMNKS Grizzly so that the X and Y turrets are on the same deck (not necessary, but it does keep the topweight down if you want).

Almost everything in naval warship engineering is done for a purpose, and so far you've been pretty good at it, but I'm struggling to find the purpose here.