NO! Why would he do this? There are several variables to consider before dumping $$$$. Just because they make parts does not mean you NEED parts. What he needs to do is drive the car first and see how it reacts then make adjustments accordingly.
Edit: and anyways, you were not “partially right”. You were referring to a Honda platform when you made these allegations. Adding a front sway bar WILL theoretically increase understeer. If the car dramatically oversteers a front swaybar will help balance it out more, but NOT by adding MORE oversteer like you claimed.