both rotors should sound equal, regardless of series of the engine. a blown rotor will still make sound but it will be extremely weak and push almost no air.

you can't simply replace a single rotor/seal set. well you could but i would strongly advise against it unless you had vast experience. breaking the seal on the engine allows everything to become slack, and to focus on only half an engine requires applying fixtures to the engine to hold tension on the unaffected half of the engine, since these engines are a sandwich design and the bolts that hold them together hold the whole engine together.

it also isn't so much a blown rotor but the apex seals are either stuck in or are broken, which usually causes the rotor and housing to be damaged in the process. it really depends on the type of seals used in the last rebuild, some seals will allow for only minor damage/superficial but OEM mazda seals usually are the least forgiving and usually result in a loss of at least a rotor and housing. you will be planning on a complete rebuild if you want to salvage this engine, otherwise try to find another running engine and just swap it.