Three comments:

The number of arguments in TrainingArguments is overwhelming. There’s no way I would immediately see that.
I don’t think that’s customary at all. Validation is almost always run in tandem with training (not necessarily step by step, but every epoch or every few epochs) to check for overfitting.
If I pass validation data to an object, I expect it to do something with that data. A default of doing nothing is counter-intuitive.