That's basically my build, although I maxed shield and have only 1 IF (will be 4 at lvl 35). 4 Riding would probably be better than 4IF if you play battle mostly, but I mostly play siege so I prefer the IF. I feel like the extra neutral nudge damage is the main reason to increase shield skill, moreso than durability or coverage against projectiles (which seems crappy with anything smaller than a Heavy Round Shield regardless of shield skill anyway).
I can't imagine having less than 7 athletics; there are so many agility polearmers nowadays that can just toy with a slow shielder. Even 7 athletics seems a bit slow with medium+ armor when fighting certain people. Builds like 18/24 and 15/27 are also good, but I feel like they only work if you have <40 ping; slashes just glance too much if your ping is higher (because you aren't positioned the way you think you are). High agility works great with stabs and picks/maces regardless of ping, though.
If I had a more reliable internet connection, I'd probably respec to 15/27. But I find too many of my swings/nudges inexplicably whiff or glance, and I need the extra PS and HPs to compensate.