Well, the issue really is that for a mere 5pts, you can enjoy 90% of the benefits of being cav. This isn't too much more reason to get more riding than that, since additional PS straight up outweighs the difference in speed bonus difference gained from riding itself, riding faster horses and having more WPF. The only horses worth riding as non-ranged cav are all 5 riding horses. However, I believe they are working on something to alleviate some of the problems, mostly such a low commitment to riding.
If you reduced lancing damage any further, the heavy lance would go right back to glance city even at +3. Perhaps the speed bonus from horseback could be reworked and the base damage penalties from horseback increased, meaning you'd need a higher speed bonus to do decent damage, but also increase the damage ceiling so having more than 5-6 riding would be beneficial.