what you say makes even less sense from a scum pov
he establishes himself as sheriff d1, claims d2 to lynch you and then... just gets fucked when you don't flip scum? too many things could go wrong, and all that just to get an inactive player out in the early game
scum ali would benefit way more from earning more town cred by whispering than doing any of this in this dp
he sees sheriff as some sort of town leader since it's the second most important role and at least one is guaranteed to be in the game, it doesn't go that well with the night abilities, but it's not exactly wrong either
By that point they'd have two recruits, and no scum deaths (most likely) by day 3. In effect, the game is over. Even if he does immediately get scum read (he would have the WIFOM defence, with the reasoning that you're outlining here), that puts them up considerably and if I read correctly, an assassin is replaceable. I'd assume he's that.
Being real with you, if you have no other mech you have to take me off the board. Whether that's lynching me or having Ekko execute me, there's no justification for not resolving me. Even with my role being strong. Now in good faith I can't actually insist anyone does that, I have my pride after all, but I can only demonstrate the importance of keeping your options open. At minimum, Ekko should be jailing Ali today. I'm simply asking that you cover your blinds pots, and don't run away with the assumption that the mech claim must be real.