The LG line of phones have a very weak digitizer setup. If you have ever worked on a G2 or G3, a small crack in the glass (where the digitizer is attached), you will lose all or nearly all touch functionality.
This is different than, say, Samsung devices where the digitizer is a part of the LED. That's why you can replace just the lens on an S4 and save money.
The LG lineup, however, is not too keen on this type of digitizer setup. So, yes, a new display assembly will solve your touch issues. Good luck!