That has been my experience with DeepSeek after the price increase. I was so used to it being so frugal, it took couple of top-ups for me to realize that it wasn't the budget-king anymore.
Deepseek 4.1 flash is back to peanuts pricing and more capable than 4 pro
The main difference I notice is that 4 pro has more "world knowledge" which makes sense given its lineage. For most tasks flash is great though and the model can just fetch the code or library information it needs.