30/9 is indeed viable.
In teamfights, use teammates as shields. Don't try to front line or your shield will break faster. Don't duel with the shield either unless you have a very fast weapon. Without tons of wpf, people might realize your stab will actually connect first and block.
Personally, I think with 30/9 you can give a single or two people amazing support. I prefer more balanced builds because I can then support entire groups of people. For example, if I'm in the far left of the mass and see cav coming to the far right, without enough agi I might not make it in time. So if you actually care about your team, missing that easy cav is simply disappointing. If you care for damage, aim your pokes better. Most people have rags for boots or paper bags for helmets.
