Are you saying the fonts you see on the PowerPoint on the iPad are different from the fonts you see as a webinar attendee on a different computer.
The fonts installed on the laptop and the Pad are bound to be different, so the fonts in PowerPoint will look different on the two devices.
If however, the fonts that show on the iPad are different from what you see as a webinar attendee on a different device, then Apple is somehow substituting fonts when you share the screen.
It is doubtful that GoTo is the problem, since GoTo is just sharing the screen that Apple has made available. GoTo is not recompiling the PowerPoint slides.