There are many diacritics in French, and not having a key for the most frequent accentuated letters is far from optimal (for instance, the previous sentence in French would contain 5 diacritics).
You'll never find an optimal layout, they're all compromises.
I've switched to US intl 15 years ago and I don't type in French any slower than I used to. On the other hand I benefit greatly from using the default layout in our very US-centric field.
