Some people say that the pre-interstellar zerg is strong, the middle Terran is strong, and the late Protoss is strong, right? If yes, please explain the reasons; If not, tell me your thoughts.

This statement is easy to understand. In the early stage, bugs are easy to form small-scale attacks because of their high outbreak speed and small population. Therefore, Terran and Protoss are both races that are easier to climb technology than bug, unlike the late Zerg, which needs many arms mutations. So relative to these, it can be understood that it is better than the zerg in the later stage. But it is unreasonable to say that the protoss is better than the late Terran.

Note that this is a one-sided understanding, because early Terran Blasting and Protoss Blasting are powerful early tactics.