I am.
It doesn’t have to be viewed as a reward. That’s not how brains work. The dopamine it objectively releases to see an indicator of progress directly result from your actions is a factor (one among many) in whether or not you view it as a reward. The latter is a more abstract concept involving conscious thought, while the latter is a base instinctive function.
There absolutely is a way to prove it, this is all very thoroughly researched and documented psychological phenomena I’m describing. Seeing an indication of progress as a result of one’s actions triggers dopamine. What one thinks about the activity and whether they “value” the indication of progress is a separate question, although the dopamine it triggers is undoubtedly one of the factors that affects how they feel about it. If you don’t find XP valuable, then clearly other factors outweigh the dopamine for you. I’m sure you’re not the only one.