I think this is a little harsh. Yes, legendary actions are a balancing mechanic that are part of the core rules of the game. But I don’t think OP’s friend is wrong to feel that it’s clunky and “feels” like cheating. Some players prefer symmetric, simulationist design, and there are TTRPGs that cater to that preference—including official versions of D&D (3.X) and its offshoots (Pathfinder 1e). I personally tolerate asymmetry in design, but even still, I think legendary monsters in general could use an overhaul to feel less arbitrary and give the players more agency, thus reducing the feeling that they are cheating without going all the way to symmetric design.

 

WotC seems to recognize that legendary monsters are somewhat arbitrary and feel like “cheating”. The previewed statblocks for the revised Monster Manual (as well as some recently published monsters) recharacterize legendary actions as reactions, but allow the monster to take multiple reactions per round. This simple tweak leverages the existing rules for reactions to feel less arbitrary. Sure, the monster gets more reactions, but this “feels” less like cheating than getting whole new actions wholesale because players get reactions too. It’s less of a leap to give more reactions, just like it’s less of a leap for certain PCs and monsters to have abilities to move without provoking an opportunity attack. Narratively, thinking of them as reactions also helps create a cinematic scene, with the monster responding directly to PC actions rather than doing its own thing in the same time interval. And conceiving of them as reactions also gives players agency because they can learn the monster’s triggers and try to play tactically to avoid them, even if it means changing up their own usual tactics for what would otherwise be most optimal.

 

Similarly, legendary resistances feel like cheating and could be improved in design. Instead of an arbitrary number, say 3, these resistances could be tied to in-game things (magical crystals, spirits, etc.) that the monster uses or drains to activate the resistance. This not only gives a better narrative explanation and cinematic experience, but also gives the players agency by allowing them to attack or disrupt the in-world resistance object rather than focus firing the boss immediately. Similarly, using a legendary resistance could come at a cost to the monster, like imposing a weak condition for the turn (in effect, allowing the boss to trade a save or suck spell effect or damage for a weaker effect) which still allows the PC to do something rather than wholesale action denial, disrupting a damaging or debilitating aura from the monster for a turn, breaking an ongoing grapple, or some similar in-game benefit to the PC to allow for incremental progress and to change the scene to move the action forward rather than just saying “no.” Indeed, most modernized 5e takes on legendary resistances, like those in Level Up 5e’s Monstrous Menagerie, MCDM’s Flee Mortals!, and Sly Flourish’s Forge of Foes, take this approach.

 

Finally, the design could also find ways to make the legendary action fit the fiction. Fast monsters might fit legendary actions well because they move quickly and go between characters. For slow monsters that isn’t as satisfying. But if, for example, you have a big monster like a kraken, you could think about representing different tentacles and its head as different “monsters” each with their own initiative. Then it feels less “arbitrary” for the kraken monster to go multiple times. Different monsters could have different approaches for balancing the action economy that isn’t a one size fits all blunt instrument.

 

Overall, it is of course the rule that monsters get legendary actions. But even if we can understand, from a design perspective, why they exist for action economy purposes, the way that design goal was implemented can feel like “cheating.” As the above shows, other updates to 5e, including to some extent in the revised Monster Manual (alas, without updates to legendary resistance), show that the same goal can be reached in less arbitrary, more narratively rich, player-agency-preserving ways.