With the caveat that "data lake" means different things to different people, I think it's important to have a repository where the raw data exists un-manipulate

With the caveat that "data lake" means different things to different people, I think it's important to have a repository where the raw data exists un-manipulated in the form that it was ingested. From the end-user standpoint that's not very useful. But that's why you have data marts that normalize the raw data into a standardized format. Ultimately though the raw data needs to remain the single source of truth. If you skip that step, and only store the post-normalized format, you're likely to run into problems down the road. This could either be because you want to change the normalization format. Or you want to use some aspect of the data that isn't captured in the normalized form. Or even you discover a pre-existing bug that affected all the previous post-ETL data.