You shouldn’t look at NAV from the lens of a stock. Higher NAV ≠ not meant it’s costly and Lower NAV ≠ cheap and more units ≠ more returns.
Now, the reason why the NAV of a direct fund is higher is because there are no commissions paid out. Now if you actually look at the returns you’ll see that directs funds always give higher returns because they don’t pay commissions. Here’s the visualization of Regular, Direct and the % difference between the NAVs.