Did you read my questions to yours above? Are we talking about the classically rigged Tornado or the modern rigged? They are pretty different beasts from what I understand, I've only sailed the modern one. Fitting out a classic T or aluminum rigged T with the modern sails and spinnaker is a very good way to get a fast boat, if you have a stiff set of hulls. Racing an aluminum masted but sports rig T vs. us in the all carbon wonder ship wasn't that different in terms of speed. Sailor ability and tactics made more of a difference.
You may need to rotate the rig at the same time as you pull on more downhaul. There is a good explanation of this by Andrew Landenberger here and copied over for your reference: https://usaca.info/landenberger-tuning-tips-mast-setup/
"The typical example is that with increasing wind the sailor will pull the Cunningham hard but not adjust the mast rotation to go with it. The effect of the Cunningham is flattening the sail, but more in the top. This allows the leech to open. The boat may feel ok but often the leech is to open and you can’t point high enough. This setup can be good in big waves but on flat water the sailor would like to have the leech standing much straighter so they should rotate the mast further back. If you go back to our original points you can see that the mast becomes stiffer in the top and can bend more in the bottom. This is therefore powering up the top and flattening the bottom of the sail. With the Cunningham pressure you can sheet on hard and point high with good speed."
Another good reference for mast tuning is Stevie Brewin: https://usaca.info/brewin-sail-tuning-care-2-2018/
There are some good Tornado tuning guides around, to make sure you are at least within nominal parameters: https://www.youtube.com/watch?v=NkQ9uPykaLMhttp://www.tornado-class.org/useful-info/tuning-guide/
Anyway, my take on your specific situation is you don't have a very good downhaul setup. You should be able to release the downhaul as soon as the gust is over or even a little before to avoid steering down too far. In the opposite situation, you should be able to quickly pull it on! We run 16:1 on the F18 and lately are running 32:1 downhauls on the A-Cat to aide with this in breeze. The crew has to be attentive on this trim setting especially in gusty conditions!
I switched to a 12:1 mainsheet this year, it was 100% necessary with the boomless DS sail on the F18 but switching back to boomless it is still very nice as in up to 15kts of breeze I can do a good deal of sheeting with one hand, freeing up the other for other tasks such as downhaul. For many years I was told 12:1 wasn't necessary and resulted in a lot of extra mainsheet. Well, after using it, I couldn't disagree more as from a crewing perspective it makes a long day on the water that much easier and by day 5 of a World Championship you really come to appreciate the little things!! Anyway, releasing the downhaul with one hand is very possible, easier with the Spinlock cleats but my last two batches haven't held with 4mm downhaul line so for the moment I'm avoiding them. Once the downhaul is off you quickly have two hands to play the main if one hand isn't enough.
In tricky conditions/big breeze the helm plays the downhaul in conjunction with the crew working mainsheet trim. We use a French rigged downhaul copied from the Nacra 17. This is rigged from the mast aft of the daggerboard to a shock block then back forward and inside the beam. We went to this from the more conventional setup (mast->turning block on crews trap->forward beam) as on the new boat (eXploder Scorpion) the daggerboard moved forward a good bit and when the helm was playing the cunni the line was digging into the leading edge of the raised weather board.