In short: Yes, no, no.
Materials do matter for what you are shooting for. If there is a specific look that say, Fuji 800Z delivers to you, it matters. Some people are more open to changing brands and emulsions (myself included) than others. Those that are more open will simply switch to Portra 800 rather than stop shooting. However, there are people that it does not work for, and while I respect them, I encourage them to try out similar films or papers from other brands to see whether any of them work for what you are looking for.
On the topic of "just as good" there are two fields. Technically, some papers and films are superior to others, but this is usually on the lower end of the spectrum (Lucky, Shanghai, Era). On the higher end, most papers/films are similar quality, but deliver different artistic characteristics.