NIF never was designed to be a power plant or have anything to do with power generation. This is something most commenters don't appear to appreciate. It's an experimental facility that, when distilled to its simplest explanation, lets us study things when you squish them really, really hard. It turns out, fusion is one of the things you can study when you squish stuff really hard - and one of the big challenges was controlling how you do the squishing (which turns out to be pretty difficult).

There are lots of other problems that NIF also studies that boil down to "what does this do when we squish it" that have nothing to do with fusion or energy production. Aside from the weapons program applications, there are experiments that take place there in materials science, understanding extreme environments ("what do these elements we believe sit in the core of Jupiter act like at those pressures?"), etc.

TLDR: Think of NIF as a lab for energetically squishing things. It's not a power plant, it's not a prototype for a power plant, it's not a pre-prototype for a power plant, etc. It's a lab for basic physics research. It's about as close to being a prototype for a power plant as a test tube in a lab full of hydrocarbons is to being a prototype of an internal combustion engine.