The suitability of a motorcycle's size for a rider depends on various factors, including personal preference, riding experience, and body proportions. In the case of the Yamaha 450WR, which is a relatively powerful off-road motorcycle, being 5'10" should generally not pose a significant issue for most riders.
Ideally, a rider should be able to comfortably reach the ground with both feet while sitting on the motorcycle, allowing for stability and control. If you have a relatively average or longer inseam length for someone your height, you should be able to manage the Yamaha 450WR without any major issues.
To get a better understanding of how a particular motorcycle fits you, it's recommended to visit a dealership or find a way to sit on the bike and assess its ergonomics. Trying out the motorcycle or similar models in person will give you a more accurate sense of whether it feels comfortable and manageable for your height and body type.
Ultimately, individual preferences and comfort levels may vary, so it's crucial to prioritize your safety and ensure you feel confident and in control while riding any motorcycle.