I'd argue it wasn't smart, you could have forced their hands a bit more to get 7 days of sick leave
Would not have passed filibuster, the strike would have gone forward, and the Republican's could have hung the blame for the vast disruptions of a rail strike on Democratic "overreaching" when there was a deal in hand that the Republicans would support.
It was smart politically for the Democrats to split it. It showed their constituencies they supported the additional sick leave, and left the Republicans to shoot it down and take the blame for its absence.
Do not get me wrong. I support additional sick leave. In fact, I support the union's demand for 15 days, not just 7. But from a political standpoint, splitting it out and letting it lose was the right play. Once it came fully into the political arena, its fate was sealed. The unions couldn't get 15 days out of rail management in negotiations, they barely got one under the threat of imminent strike in September. They only way they possibly could have gotten it was to have been allowed to strike, causing vast disruption to the economy.
That does not change my opinion that rail management has been unconscionable throughout this.