I do not think tornados and cyclones are treated as the same phenom, differentiated merely by size.
Off the top of my head:
- cyclones are driven by the heat soaked up from oceans, tornadoes by land (though waterspouts get their energy from water)
- cyclones are formed and move at least in part due to Coriolis forces, tornadoes are not*
*although TIL, that tornadoes
do have a preference for CCW rotation in the N. hemisphere
Of course, there are distinctions of scale: size, duration, power, etc. but those are quantitative, not qualitative distinctions.
Still, one would expect that - if they were the same phenomenon - we should find a continuum of events from the smallest F1 tornado right through the largest Cat 5 cyclone. But we don't. They are only at the far ends of almost any metric one might care to use - with a big gap in between. This suggests (to me) that they are independent phenomena at their source, even if, superficially, they both result in high speed, rotating winds.
I'll wager there isn't a single case in history of any event that fell in a grey area where its status as a tornado versus a cyclone is debatable.
https://www.diffen.com/difference/Cyclone_vs_Tornado