Imo using a text based tool for presentations is really counterproductive because presentations should use as little text as possible.
For me currently, libreoffice impress is actually the best option because it has all the necessary features (wysiwyg style editing, svg support, latex equations, some animations).
Up to the introduction of quantum mechanics imaginary numbers where only ever a theoretical tool and any calculation in electromagnetism, mechanics or even relativity can be done without them.
Also, any measurement you can make will always result in real numbers because there is no logical interpretation for imaginary measurements (a speed of 2+i m/s doesnt really make sense)