My piano is too "rigid". More details inside!?

You need to find a piano technician who can do MORE than tune - it sound to me like your piano needs action regulation and voicing. Most piano techs, if they found this is what it needed, would have TOLD you so - unless you said "All I need is tuning.". Only you can speak up and say that the action is stiff, you do not like the brilliance of the top octaves, etc. Unlike tuning, these procedures only need to be done every few years, at most. Again - this something that I cannot diagnose from a distance, but only surmise form your description. Call someone GOOD today. Kawai is a decent home piano brand, and you should not have to be dissatisfied. Is this REALLY old? Maybe this was never done. And even NEW pianos often arrive with the need for adjustment. Pick up the phone - no reason to put up with this, when it can be fixed. Then - pick up your checkbook - it is going to be a little investment.