Cost would be a big issue as you probably could build many more Leopard CV's and add there squadrons for the cost of a single Mule PWS. And there are a ton of dropships to convert if you have the facility's. But the big issue is how best to use these to raid outside the Republics walls. Do you want a few hard hitting PWS's or large numbers of CV's with literally thousands of tons of aerospace fighters?
scaling applies here-with sufficiently good information, you don't need maximum force on every operation, there are any number of good reasons to send a Leopard, or even a converted Scout (i forget the name), mostly to targets or regions where you don't actually need to make a BIG impact, or where the response is going to be in some way disproportional (too little, or drawing in radical amounts to leave some other target vulnerable).
for you 'mech types, such situations can be equivalent to using a bug 'mech instead of a fast heavy-because the fast heavy is overkill for the job, or because you intend to use it somewhere more critical, but need the distraction.
one of the major flaws from the FC3062 game, was how readily players threw monster battleships in monster numbers at unimportant targets because there was no factor preventing it...while I stymied at least one of those by scattering fractional-point value units into empty hexes they had to cross. This actually stopped the in-game Star adders from finishing off a thirteen world section of the Lyran Commonwealth for a turn, because his vast fleet of leviathans had to stop and eliminate my collection of cheap jumpships one at a time.
in logic, the reason would work out to needing to prevent a fleet-in-being from disrupting his supply lines on his invasion, and he didn't REALLY know how many ships i had (i kicked ass on the intel roll) the point being that in terms of fiction, the knowledge tehre IS a raiding fleet, and it IS behind your line of advance, changes how you can or should run your offensive. It slows things down, forces efforts to locate or protect against it, changes the tempo and can potentially shift who has the initiative on the strategic level...
even if their fleet is 'on paper' significantly weaker. An in-canon example would be the Taurian Navy's fight against the Davions in the malagrotta affair, and what it took for the Davions (with Star League and Terran Hegemony help) to end that threat.
Naval in space is strategy and psychology. If you can work the enemy's nerves you can force him into sub-optimal positions whether over-distributed to try and 'catch' the raiders, or over-concentrated into convoys that move too slowly for the advance...while leaving his own position under, or not, defended.
The central theme of naval raiding isn't territory claim the way it is with ground warfare, it's about disruption, distraction, and positioning, influencing the battlefield and influencing outcomes by working the other side's nerves and creating openings.
For that kind of work, the only important feature is for your units to be
actively doing it, so a broad distribution of mediocre units actually can be significantly better for the purpose, than a tight concentration of powerful ones. If your opponent can only patrol x number of systems, have a raiding force that can strike X+1 number of systems-he either must leave something undefended (which offers you opportunities to strike something vital) or he must reduce his coverage. (you can't fractionalize a McKenna, it can only protect one location of a system at a time.)
your main focus here, is to force him to deal with a threat along his supply line, because assets devoted to that, aren't supporting the offensive.
