Yeah, it makes a bit more sense in situations where the infantry can't easily be just ridden down, for instance if they're protected by a dense square of pikes. Then you can send skirmish cavalry to harrass them and potentially cause enough damage or confusion that the heavier cavalry has an opportunity to charge home. If nothing else the presence of nearby cavalry at least meant that the musketeers couldn't spread out to skirmish and had to remain very close to their pikemen at all times, reducing their overall firepower and leaving them more vulnerable to artillery and other musketeers. Curiously during the pike and shot era you seem to see a lot more experimenting with close coordination between cavalry and infantry, for instance deploying squadrons of horsemen in the gaps inbetween pike squares where they could keep firing while also watching for opportunities and keeping the enemy on their toes.
Pistols and carbines seem to have been also considered more useful when attacking infantry who are behind some obstacle such as a ditch, hedge or sharpened stakes. Though it tends to be much harder to break an inanimate object's morale.
One argument i've heard goes that as the wars dragged on, especially after the russia campaign, France was starting to suffer a serious shortage of good horses and that this may have been part of the reason that the french cavalry performed so poorly at Waterloo.
It does seem that sword and pistol cavalry who fought in very dense, squadron formations were considered able to worry less about the quality/price of their horse overall. There was also napoleon's quote where he claims something along the lines of 1 mamluk could defeat 2 french horsemen, but that 500 french horsemen could defeat 1000 mamluks, i.e. when large numbers of horsemen are fighting, individual skill becomes much less important than learning good discipline, cooperation, and tactics.
It might also have to do with just how well you do utilize your most talented troops. John Cruso's manual, for example, repeatedly stresses that when fighting other cavalry, whether you have harquebusiers, cuirassers, or lancers, you should always keep 10 or so of your "best mounted" troops in reserve with a good officer. The idea apparently being that if the main body of horse gets routed then the fastest enemy horsemen will pursue, at which point your best mounted troops can intercept them and try to either punish them for breaking ranks to pursue or scare them off and then hopefully manage to escape without taking any losses themselves.