Back to basics: it’s the cook ánd the kitchen
The cook: you need to be able to judge your own work unbiased and hear what it needs and know how to get there.
This has nothing to do with the “right” daw or certain plugins. You need to know when to use an EQ, when to compress, how to compress, how to EQ, how hard you can drive a limiter, understand target loudnes, understand the LUFS short, mid and intergrated of compareable tracks. Amongst many other skills. All of this can be perfectly done with the standard set of Cubase plugins.
The kitchen: your room and monitoring need to be top notch, they need to be trusted 100%, full range and your output needs to translate FLAWLESS anywhere.
Choice of DAW or plugins has NOTHING to do with this. Neither does stacking a pile of plugins to make things sound “phat” that’s NOT mastering. It’s actually degrading to talk about “mastering” in such a way.
If anything, start with REW and start working on acoustic treatment and response, once that is in place to a certain level and you know HOW to work the standard plugins, it’s time to look further.