TS
Mullah regime and Arbi tyrants, religious and secular, are tremendous assets to the Israeli narrative of themselves as a Island of "Democracy" in a oceans of barbarous brutes who not only brutalize their own but represent a mortal threat to Israel -- So long as these are no real threats, Israel has zero incentive to seek their removal.
The Iranian narrative, for the larger community of Muslims, is quite similar, the Iranian realize there is no possibility of "victory" over the "Zionist entity", however, groups such as Hamas and Hebzbollah, have more to do with political and social failure in Lebanon and Palestine than as symbols of Iranian street cred as you put it.
As for the the issue of "mehdi" is concerned - it does not do for adherents of confessions in which the Mehdi, Messaiah and Meshiyuh are essential elements to be dis'ing the other adherents or the doctrine itself