The reason rogues are ineffective against undead (specifcally skeletal) is because they are crippled to always used stupid daggers, and skeletons need bashing/crushing damage to be effectively countered.
Giving rogues some means of generating a concussive force (say, an explosion shock wave), would solve the issue.
I have always chafed under such rule restrictions, because to me they make no sense. A rogue might have a weapon proficiency issue with using a billy club (doubtful, ruffians use them all the time. It is the weapon of choice for jackbooted thugs IRL.) but saying outright that they cannot figure out how to club something is downright absurd. Saying a wizard cannot channel a spell through a melee weapon makes some sense, so I can tolerate glass cannon shenanigans, but I feel rogues should be able to use any simple weapon, and rather than say "no, daggers only!" I would give them a "Simple weapons" proficiency. (Simple weapons are under 2.5 ft long, have no special requirements for dex or str, and are of mixed type bash, bladed, and special. Special being for things like a length of chain, or a short whip, like a riding crop.) This would enable things like using a frying pan, a billy club, a blackjack, etc. Due to the weapon size restriction, it is still a close combat specialization, with all the drawbacks that has.
But no, IMO, the official rules are way too anal about "NO! Thieves and Rogues USE DAGGERS AND BOWS! ONLY DAGGERS AND BOWS! *screaming hissyfit tantrum*"
I cannot stomach that nonsense, personally. It makes sense that somebody that specializes in stealth and finesse wont be using a 2H claymore. I get that. But you know what a
blackjack is? It was designed for stealth elimination of guards and subduing marks for performing a mugging (originally- It has since found some modern love as a self-defense item). Exactly the kind of thing a rogue would be using. It is essentially a little leather bag filled with lead pellets, attached to a handle. It deals blunt impact trauma. Similar in nature to a sock filled with a bar of soap. It would be super effective against skeletons.
But No. "Rogues use daggers! (tantrum!)"
Needless to say, I feel it necessary to house rule that nonsense out of existence.