Bargaining power would refer also to the power to obtain favorable non-salary conditions (and to other types of negotiations), but "low bargaining power" certai

Bargaining power would refer also to the power to obtain favorable non-salary conditions (and to other types of negotiations), but "low bargaining power" certainly does imply "easily exploitable", yes. It's not entirely tautological - it does say that they get a poor bargain because they're in weak position to bargain for more, which is kind of the default cause for that (at least in economies with a mostly free labor market - if the salaries aren't set by market, then bargaining power is not that relevant), but it also clarifies that the poor bargain didn't happen because of, say, lack of trying or lack of information or fraud or pure randomness, and it also implies that their situation won't change unless either the main factors weakening their bargaining power (mostly the "excessive supply" issue) change or they get handed (e.g. through legislation) a better bargain than they would be able to negotiate. The power to strike is relevant as the capability for collective action does grant a somewhat higher bargaining power that they would have otherwise, other things being equal; but of course there are many professions which have a higher inherent bargaining power without even attempting to organize, simply due to having better alternative employment opportunities.