You have a great concept of how important Dressage work is for both horse and rider. Many GP Jumpers spend 5 - 6 days a week doing only dressage because of how important the fundamentals are for being sucessful in the Jumper Ring.
Most Eventers at mid to upper level spend majority of their time training in the Dressage ring, for the same reason - because without it, you have many holes in both horse and riders education and training.
So, be proud of yourself for knowing how important it is to keep riding Seat Into Legs Into Hands To Soften - I do the same. I spend 99.9% of my time doing Dressage with my horse, and I ride alot of the same Seat Into Legs Into Hands To Soften, as shown to me through a few Olympic Level Eventers in Clinics - BUT I fall into the same scenario with my guy when we Fox Hunt.....I can use all the seat I want and I can incorporate all the leg I want. I can ride this way till the cows come home - but when it comes to Fox Hunt, all that goes out the window because his mental state is not there.
So - I say, use what you need to get the job done. As David O'Connor says "Train/Ride at home in a snaffle, but use what you need to use at a comp to get the job done"
Look at GP Jumpers - those horses know minimally level 3 dressage, because of how much time is put into them in the discipline of dressage, but at comps, it's a different story. These are big, hot, strong, powerful horses who know their job and get it done, and those riders use what they need to use to get the job done.
So - through thorough discussion with your Trainer, and through thorough research on the bit, and while yet you continue to ride how you should ride and continue to train through the theories of Dressage - use what you need to use at a comp, to get the job done.
When I ride my guy at home, at comps, away at other barns - we are perfectly fine. I ride Seat Into Legs Into Hands and incorporate dressage in our daily riding. I use a basic French Link Egg Butt Snaffle - but when we Fox Hunt, I put a 3 ring french link elevator in his mouth, because of how strong, powerful, excited he gets in that situation.
All the best!