Its not really about the density that makes it softer or harder. Lead is more dense than steel and is softer, but tungsten is more dense than both but much harder. Its more about that lattice structures and how each system deals with dislocations.
Also steel is a very vague term with a huge variety in types and characteristics. With different microstructures like spherodite, bainite, martensite.... and different heat treatments and cold work input. Basic A36 construction steel has brinell hardness of around 180 and aircraft grade titanium has a brinell hardness of 330.
Long story longer, the steel vs titanium comparison is much more complicated than it appears. In this case the steel used is hardened either through carbon addition, cold work input or alloy, and the titanium is softer because it's theoretically modified less.
