Anyways, using only GT output and ship displacement (tonnage) to judge the necessity of engine power is wrong. The hull shape (draft, beam and length) is the decisive factor that must be taken into consideration. I find this is missing in the pages of debate. Same tonnage, but smaller cross-section (longer length) will need much less power to push to the same speed.
Also to remember that, IEPS has the deficiency of mechanical to electrical to mechanical conversion, while the mechanical drive has the gear box. Both deficiency is at less than 5%. So there is no way IEPS ship require significantly lower (down to half) power. The only impact on that scale (tens percent) is the hull shape.