I think activism works, but I find it's sometimes hard to visualise because often it's about lots of tiny acts rather than the big sweeping statement ones (which are obviously very helpful too).
I definitely feel that things I've contributed as an individual have made a tiny difference in the right direction. Sure, we might be in a similar situation now if I personally hadn't been involved as I'm only one person, but each person's contribution helps.
It's similar to the question "will my one vote really make a difference to the election outcome?".
In addition to the collective power individuals can contribute to a larger campaign, those tiny bits of activism we all probably do on a regular basis also help to change things for the better.
You might not regard all those times you've voiced your concerns to a friend, boycotted a brand, made a complaint, challenged someone's ideological language, etc as activism, but that is what it is, and if it makes even one person consider things from a different perspective, it all helps in the long run.
One of the things I like to think about when considering how best to use my time on this stuff is to consider my existing skills and interests and capitalising on the areas where I feel my efforts can make the most impact while not being totally draining.
So for me, I'm not going to be getting up on a podium or organising a rally any time soon as that's just not my thing and other people are much better at that stuff, but there is plenty I can do behind the scenes (research, drafting, etc) that some of the more outgoing people would find incredibly tedious and would hate to spend their time on. So it all balances out.