Steel Keel vs.Lead Keel
This is a short term maintanence vs long term maintenance issue. If you start out with a properly prepared iron keel, meaning sand blasted to raw metal and then protected by a heavy barrier coat of epoxy and epoxy based fairing material, you will have a coating that could last 10-15 years with minor touch up on each haul out. That is about what the lifespan of the fairing materials on exposed lead the only difference being that you don''t need to be as rigorous about touching up the Lead.
If you have an encapsulated keel you can apply a barrier coat to the encapsulation and that barrier coat should last for a very long time if the coating is not damaged. The problem with an encapsulated keel is that it in a hard grounding the encapsulation envelop can be badly damaged and even drive the ballast keel up through the bilge membrane. Even when the damage is less significant once water enters the encapsulation envelope that is the often the beginning of the end for that boat because delamination will occur between the encapsulation and the ballast keel. That is a nearly unrepairable damage.