Tens of millions of zerk fittings have been successfully used over the past 80+ years on every conceivable type of machinery that needed periodic re-lubrication of critical bearing surfaces.
There is nothing inherently wrong with the design of a zerk-type grease fitting.
If your grease gun was copiously leaking grease from the nose of the chuck every time you pumped the handle, either you didn't have the chuck fully engaged on the fitting, the fitting was damaged, or the chuck on your grease gun was damaged.
If you had the same leakage problem on multiple zerk fittings, most likely your chuck is damaged, or has sand or dirt preventing the fingers from gripping the zerk fitting properly.
There is a rubber seal in the chuck that gets pressed against the nose of the zerk fitting to prevent grease leakage. If this seal is nicked or torn, or contaminated with embedded dirt or sand, it will not seal properly and will leak.
Disassemble the chuck, and clean everything with solvent. Inspect the three gripper fingers for any type of damage, and especially the rubber seal for nicks, tears, or embedded contamination.
And ALWAYS carefully clean each zerk fitting before attaching the grease gun chuck. Little rubber caps are available to snap over the zerk fittings to keep them clean and corrosion free, and will even stay on U-joint zerks.