Not really. An 85 ton Starship fueled in LEO can use Oberth effect, get to Mars just as fast, and land directly on Mars.

Your deep space NTR has engines that weigh way at least ten times more, while providing only a fraction of the thrust, and also has to push not only hundreds of tons of radiators, shielding and heavier tanks, but also a lander since NTR doesn’t have the thrust to climb out of any significant gravity well. And also is going to have substantial propellant evaporation by the time it reaches Mars since it can only achieve that ISP with hydrogen.

Oberth effect is useful for every reasonable trip - since every reasonable trip either originates or ends deep within a gravity well. (And being in orbit deep within a gravity well implies being at high velocity) It's why you make an escape burn at periapsis and not apoapsis.