Original commenter might be a bit behind on many things but this is actually my day job.
Do you have a source for the reliability claim? There are so many good old transformers deployed around the world. Many of them working for 10s of years without a replacement. I'd be suspicious that a buck converter will have longer MTBF than oil submerged transformer.
Also, I don't see why it is mentioned here but NREL estimates the cost of grid scale inverters (for installations of 100 MW) to be 5-10x more than what was mentioned. [1]