The result, with either sort of oscillator, was a synthy sounding kind of wave, with a 'warmth', or a deep buzzy bass, or whatever seemed appealing. In the early 1980s, Yamaha came up with a twist on the oscillator method. In whatever is generally called, wavetable synthesis, a sample of an instrument is taken, with certain acoustics, and so on, so that when a note is triggered from MIDI, the synth will play the part, but best within a certain range of notes, as if someone were really playing the instrument. But as it is one aspect of the instrument, being played in a certain way, it really, ultimately, can't capture all the subtle shades and variation in sound that one gets when playing the instrument, itself. The Roland GS synths come in all sorts.
Some older ones play only a few channels and notes at a time.
As noted above, there are certain ways of generating basic tone, but there are also certain ways of sampling and producing wave table instruments. Not all synths seem to have the same 'flavor', with their built in instruments, and particularly as one goes back in time with changes in synthesis methods. One synth might play one sort of song well, another might be best for another type. So the Roland works for hard rock, and heavy metal MIDIs. It would just all depend.