I'm curious about where you read about any O'DAY 27s that lost their keels. This would be a pretty major shipwreck, since the 27 had the keel molded as part of the hull, the lead ballast was inside the keel. There were no keel bolts on the 27. The later (1986-89) O'DAY 272 did have the lead wing-keel bolted on, but I have not heard of a rash of those coming off, leaking yes.... but no failures that I've heard of.
The 34 was originally designed to have a bolt-on lead keel fin, but the beancounters at O'DAY substituted a cast-iron fin for the first few model years, after which the lead fin was finally phased in.
Most bilge pumps will only bail down to about 1/4" of water depth (at least the ones I've used) larger ones may leave more.