Well, just for reference about armor usefulness:
Naked/Mithril Armor -> All Unmentioned Clothing Types -> Trenchcoat -> LCS Body Armor -> Police Body Armor -> Army Body Armor -> Heavy Body Armor
Bunker Gear has some level of protection as well, but it isn't that useful overall. Even against fire damage it fails fairly quickly, and bullets aren't really stopped at all.
It's not quite as simple as all that.
First, Trenchcoats work as regular clothing armorwise. Trenchcoat being armor was from an ancient version, and has persisted as a urban legend.
There are actually two types of police armor: Regular and SWAT. SWAT is better.
Finally, the above diagram does not take into account
where the armor protects. Bunker Gear is arguably useful simply because it covers all body parts, whereas SWAT armor is the first armor that protects the head. Headshots tend to be deadly without armor that covers the head. That is why Bunker Gear is harder and more expensive for tailors to make.
So, Bunker Gear actually is useful for high-health characters, as it allows them just enough protection to survive headshots regularily. Anyone else would die from headshots with or without the protection of bunker gear, so it is best to give them LCS body armor or Police Armor, so they can at least survive shots to the torso.