Technical differences between workstation and normal video cards for a creator?

Usually, workstation cards like the Titan have a bigger VRAM. Bigger VRAMs specifically help game developers store larger texture files, but at the same time, also allow better video work. For Illustrator and Photoshop I'm afraid this distinction means nothing. Any modern video card with at least 6 (recommended 8) GB of VRAM will suffice. The RX 580 you're talking about is actually a great option.

APUs are also great I'm not sure why you're getting lag. Maybe the version has bad optimization? Has happened with me and I won't rule it out. Test your APU with other versions first. Also remember the system RAM, allocated space for scratch disks, monitor resolution, HDD/SSD quality, and finally the processor also need to be factored in. In the case of your APU the problem might be the cores/threads count (eg. first gen AMD APUs are not that great for handling modern apps), and not the integrated Radeon graphics. Same goes with Intel processors.

If you're looking for the differences between the video cards I recommend the guide on types of video cards on Spearblade: Types of GPU. The latest Titan on the other hand is more geared towards machine learning and AI than graphic design and video editing IMO. Check the official page, always, before you make up your mind: Titan V.