Complex sentence: When the final version of the Sparviero, the SM.79 bis, became available, then it replaced the SM.84, while as bomber it was inferior to the CANT.1007 ter, especially at altitude (SM.84 was almost unflyiable over 5,000 m).
Split into simpler sentences: When the final version of the Sparviero, the SM.79 bis, became available, the SM.84 was withdrawn. In the bomber role it was inferior to the CANT.1007 ter, especially at altitude (the SM.84 was almost impossible to fly above 5,000 m).