You are terribly wrong. We are talking about tanking raid bosses, not dummies. Even with 7.5-14.99 expertise you have extremely reliable hopo regeneration. You are simply trading hps, dps, holy power and absorbs for a tiny bit of "reliability".
Neither of the options are a clear winner, neither is completely wrong, depends on your situatio. It is a matter of throughput vs covering the slack if you have bad HoPo planning. For any experienced protadin, the reliability of not being expertise capped is irrelevant, which means that you are comparing throughput vs less throughput. In those cases for experienced paladins, the throughput is always better, which makes haste>exp for experienced players, which is why a general consensus in these forums feels like haste>expertise for 10 man content. Still, with current gear you can reach 15 exp even with haste>exp priority which means this is only really relevant for people gearing up at the moment.