Ah yeah, the famous "ADC win midlane and mage don't do anything" myth.
There is very few mage that should ever loose to a tristana early game, even with warlord, her sustain isn't enough to survive well made rotation or poke by a mage.
Tristana roaming is SUPER risky, she is a squishy target and if she use W to escape an interception, she lost time, mana and anyway to survive an other mistake other than loosing her flash.
Her itemisation is actually no problem for you as:
You will outdamage her early game, IE is a powerspike so she does good damage while you will have good scaling (except particular mage) right off the bat, the moment she has BF (for example), you will have a lost tome, boot and refillable potion to just have an easy time in lane.
She rush hexdrinker? Enjoy her having a delayed powerspike and almost no dmg.
She rush sustain? Enjoy her having no defensive option and almost no dmg.
ADC mid is a myth, very very few of them have strong win rate and are new in mid.
Lucian and Corki are the two famous "ADC mid laner" who always have been strong here, hell, Corki is a "Weak early, heavy late game" magic dmg champ and Lucian has a lot of weakness already.
Truist me, I saw tristana jungle, I saw twitch top and I will tell you why they could ever win or not be trashed out:
Because the people facing them either sucked or didn't punished them accordingly.
Please play a tristana mid, I will enjoy playing almost any mage against her easily.
Please play an ADC jungle, even twitch, I will enjoy playing Xin, Lee sin, Reksai, Elise and so many jungler to just bully you in your jungle or counter gank you.
ADC scaling is incredible, that much is very true and ardent is still very annoying, but don't go with your ADC mid BS.