Biden is the president of the United States. He should obviously be privileging the welfare of the vast majority of working people over one specific group, and a rail strike would be a disaster for working people. Hopefully the unions can still negotiate a good deal, but that shouldn’t be the president’s primary concern.
If it's Biden's job to prioritise the many over the few, then - if he is to interfere in the strike - surely he should do so on the side of the larger group (the workers). It's within the federal government's power to force a deal that the current management doesn't like.
Doesn't that need to be done through legislation though? Which means you need 10 Republicans to vote for it or to abolish the filibuster, neither of which he can do.