Should You Add a Second Tool For Best Results?
If you did deep enough through Corel marketing material, you will see that Paint Shop Pro is considered the "consumer" product and Corel PHOTO-PAINT is the "professional" product. Wouldn't it make sense that the professional product could do everything in the consumer product and more? Of course it would, but that isn't the reality of this situation.
One area where PaintShop Pro has more tools is if you are a photographer needing to work with your images. An example would be the various High Dynamic Range tools. There are no HDR tools at all in Corel PHOTO-PAINT X6 where PaintShop Pro X5 has multiple way to get an HDR effect. Just this one tool could justify the cost of adding PaintShop Pro X5 to your toolbox if HDR is important to you.
Both Corel PHOTO-PAINT and Corel PaintShop Pro included the ability to work with RAW files. Yet neither of them use the superior technology found in Corel AfterShot Pro. Again, I can't give you a good explanation why Corel doesn't use their technology in their own image editing products. I can simply tell you that if RAW-editing is important to you, then it makes sense to have AfterShot Pro in your toolbox. Neither include the amazing brush technology included in Corel Painter. Yes, I strongly believe Corel should use the same technology across the whole line of products.
Each of the scenarios I've described is comparing various tools from Corel. We can also compare these products against products from other companies. There is no single right answer for all users. You simply need to look at the tasks you need to complete and then determine the right tools for you. In some cases, the best answer may be to use multiple tools as it will give you the best results.