I think Utada has gone from strength to strength with each album she's done.
You've got to remember she was 15/16 when First Love came out, 17 with DISTANCE and 18 with DEEP RIVER. So as she's matured she's obviously sung and focused her style on different things that have inspired her.
And she's dabbled in R&B stuff recently too (as per First Love) and gotten back to her roots in some newer songs, but that's obviously not her focus or priority any more.
I doubt she's taken the hiatus to focus on music - she said that wasn't her intention, although she is continuing it, I doubt it's her main priority during this time.

I can't say I agree with you, I think Utada is still the same as she was, releasing decent and catchy songs, but then again, that's my opinion and if you feel differently, that's obviously yours.

But ultimately, no, I don't think her hiatus is to focus on music - she's confirmed her intentions during said hiatus already.