That last sentence is a total strawman. Unions are not there so you get everything you want. They are there to turn individual negotiations and protection into group and collective one. So it's not just a single junior programmer fighting for their rights, but potentially all company SWEs fighting for this junior programmer rights.

If Meta faced a complete strike similar to writers' strike, their workers could achieve similar goals like writers did.

Or not - but nobody promises it, that's silly.