Even at high levels, a party without magic weapons struggles against a rakshasa (believe me, I know). With magic weapons, yeah, it probably goes down pretty easy.Still, that curse is nasty--no save and two chances per round to apply it. I think the rakshasa's CR needs to be considered in the context of an adventuring day rather than a single encounter. It lets some minions engage the PCs, darts in and tags half the party with the curse, then casts invisibility and bugs out. Then it continues to harass the party one encounter after another with illusions, dominate person, and so on and on. With the curse in place, the party's staying power is seriously diminished if they don't have remove curse available.
I'm still not convinced it lives up to its CR, but it does have some vicious tricks up its sleeve.
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