In my opinion, and in observation of most modern popular music, sparse mixes sound really good and are in style right now.
However, three instruments is really, really sparse. Assuming you count the drums as one instrument, then you add bass and vocals? What about miscellaneous percussion, pad, lead synth, supporting synth effects, and miscellaneous effects?
Your total count of instruments will always vary by song. It depends what the song needs, how much room the vocals need, how large of a frequency range the instruments occupy, etc. You can add more instruments by carefully EQing space for them. Smart panning frees up space too. Doubling instruments, for performance thickness or to mix tonality, is a useful tool too. And often a song without much effects can have more instruments, where as a song that heavily relies on reverb and delay to get its vibe maybe doesn't have space for many instruments without burying the reverb and delay.
You need to decide how many instruments to use yourself. Be creative and be yourself. Use your own judgment. But, if you find your judgment off in one direction, mentally calibrate. I have to remind myself to make tracks more sparse, and I'm pleased with the results each time I do this.