Normally Tropical Cyclone Tracy would have been a category 3 tropical cyclone when it hit Darwin on Christmas Day 1974.  However the reason why it was stronger , a Category 4 cyclone was because twisters or tornados had developed inside Cyclone Tracy when the cyclone was about to make landfill.  Had there been no tornados in the cyclone it would have been only a Category 3 storm.

The houses were weak anyway so  they would have been blown down anyway.  But what surprised me most was some concrete walls was blown and steel power poles were twisted.  I don't believe Cyclone Tracy ever made it to category 5, instead tornados had developed inside Cyclone Tracy and I believe that tornados inside the cyclone were more to blame for the mass destruction of Darwin then the cyclone itself.

I haven't been in Tracy myself, but I have been in a cyclone of similar strength, and that was Cyclone Aivu which hit Ayr in 1989.  It was a category 4 storm and I saw the eye of it, but I didn't see any tornados spawned from the cyclone cloud, so because there was no tornados that i was aware of, the cars weren't blown away or the steel structure twisted.  I think tornados made all the difference in destruction.  Aivu had wind speeds of up to 230 km / h while Tracy had wind speeds of 220 kms, but increased to 250 kms because of tornados, and tornados probably made Cyclone Tracy look stronger then it really was without tornados.

Tracy was really a circulation of storms around the eye, and storms around it probably triggered tornados inside the cyclone.  It was raining at times in the lead up to the cyclone as Tracy approached the coast.  As it was a La Nina year there was plenty of humidity in the build up and in the lead up to Tracy and Selma and the high humidity probably caused a higher number of storms than usual and the chances of tornados were higher.

Had there been no tornados in Cyclone Tracy I am pretty sure  the power poles would not have been twisted or the cars moved away.  So a combination of Cyclone Tracy and tornados inside the cyclone probably contributed to the mass destruction of Darwin.  Cyclones themselves without tornados would not have twisted thick steel structures or break down concrete walls, not even a cat 5 cyclone without tornados.

I am doubtful if there would have been less damage if tornados didn't form in Cyclone Tracy, because it was moving at 6 km / h and was small but intense.  I don't believe most people witnessed tornados in Tracy because it was too scary to see, and too dark to see, poor visuality, the tornados could only be seen in flashes of lightning, and because the tornados and cyclone tracy itself probably contributed to the mass destruction of Darwin.  But the houses would have been blown away anyway because they were of weak structure and weren't built to withstand the full force of cyclones.

It's possible there was also some tornados in Cyclone Monica and Ingrid, but even if they have occurred, they cannot be seen because even in daytime the thunderstorm clouds associated with cyclones are very black and Cyclone Ingrid passed Tiwi Islands at night and Cyclone Monica crossed the coast in a isolated area north of Jabiru also at night.

William Walker