I would disagree, and I personally know people who have unionised IT workers. I also personally know people who have unionised workers at small companies. I don’t understand why you would say unionisation is not relevant to you? If you’re a worker then it is relevant.
Well, fundamentally capitalism involves the deprivation of the means of subsistence and production from one class so that they are forced to sell their labour-power to the capitalist class in order to obtain the means of subsistence. You could define that as “mistreatment” or not I guess, but whether or not you do, personal treatment by your capitalist does not change the form capitalism takes. Workers’ power comes from combining. Capitalists are already combined—they work together to keep wages low and prices high. Unionising only levels the playing field in that regard.
I’m not saying that you should always focus on unionisation in every situation—sometimes there is more important political work to be done. But if you have nothing else to do, it’s often the most accessible starting point.