As you know there is one knob inside each oscillator section of Serum named "WT POS". It allows different waveforms to be selected by automating using ENVs or LFOs.

I saw all of the pre-installed factory waveforms. The only major thing that is changed in them is frequency characteristics. For example if you take a look at "Acid.wav" file in "\Users\...\Documents\Xfer\Serum Presets\Tables\Analog" folder, you'd see that it's just some sort of sine waves that its frequency is being changed in the next periods like FMs.

As you know "WT POS" knob's duty is controlling which period or waveform to be played.

Of course Serum allows generating arbitrary waveforms by clicking the pen icon inside the waveform window but it's not the main factor that distinguishes it from other synths because there are bunch of free tools that generate any waveform that you need even better than Serum.

So the result:
I think with having a few knowledge about manipulating the waveforms inside other synths we can simply avoid using Serum or other wavetable based synths. I mean we can omit the wavetable synths from the categorization.

So just 2 synths remain at the top. Sytrus (FM+subtractive) and Harmor (Additive+subtractive).