In a nutshell, on smooth city streets at city type use , you won't notice the difference , except in potholes ot maintenece dips. There the extra mass is hard to tame , but as it only occurrs once , it would be annoying but not much else.
At higher speeds and on rougher surfaces the extra mass will be more noticeable. Multiple modulations will be much harder to contain especially as the emotorcycle crowd seems to have bypassed decades of suspension tech and gone with very poor solutions. Poor quality damping ( ICE equivalents aren't immune from this one), heavy suspension components and poorly designed chassis and linkages ( read simple single pivot rears mostly) are the big problem. The heavy unsprung mass contributes to the problem. Could a hub motor be designed to work sufficiently well. Of course!. Has it yet...mostly no.
Part of the problem also is that the hub motor unsprung weight is also a more significent proportion of the total system weight ( bike and rider). That also makes it more difficult to control. On a car the hub/suspension weight even with motors on each wheel is a tiny proportion of the total system weight, making it less noticeable.
The gyro effect on handling is more complicated. If you have as much motor mass as possible close to the axle , it will be less of a problem.
The bit few talk about, is the effect of the rear wheel mass relative to front wheel mass, and the consequent gyro interactions. To turn a two wheeled caster steering vehicle, the front gyro has to overcome the rear gyro ( which is trying to keep the bike upright). With a heavier rear the front input has to be greater to bring the bike back from understeer to neutral.That requires a rethink to get it to handle properly.
