Even without owner support it's easy to get something landmarked if the HPC chooses to do so. There are seven different criteria to landmark a building. With owner support, you need to meet two of the seven criteria, without owner support you need to meet four criteria. But it's relatively easy to check four of those boxes if the building's old enough.
(1) Its value as a significant reminder of the cultural, historical, architectural, or archaeological heritage of the City, state or nation.
(2) Its location is the site of a significant local, state or national event.
(3) It is identified with a person or persons who significantly contributed to the development of the City, state or nation.
(4) It is identified as the work of a master builder, designer, or architect whose individual work has influenced the development of the City, state or nation.
(5) Its value as a building is recognized for the quality of its architecture, and it retains sufficient elements showing its architectural significance.
(6) It has distinguishing characteristics of an architectural style valuable for the study of a period, method of construction, or use of indigenous materials.
(7) Its suitability for preservation or restoration.
Source: I've helped landmarked a number of buildings in Jacksonville.