Ohhh Sonya is whirlwinding through my minion wave! Let's move towards him so he can Q my ass and Slam me out of lane! Said no one ever.
You can do at least 12 CLs with just your mana pool, not counting passive mana regen, regen globes and the mana return from the level 1 talent. Do the math, that's more than enough to push pretty much any ranged character out of a lane. I also don't see how Resilience stacks are relevant when you're talking about mana, but even then the bounce range on CL is pretty substantial and the chance of hitting only the person in your lane is slim but even if it happens it's still worth it.
Also, lol if you think you can Flamestrike any non-retard Thrall without stunning him first. Did you ever try out Thrall? The range on CL with the level 1 talent (which pretty much everyone gets) is bigger than the range of your AA and Living Bomb so your only hope is to hit him with blanket Flamestrikes which A) won't happen vs. anyone with a brain and B) he'll just heal the damage back up through his trait. The fact that you think that he has to run into his minions for you to conveniently Flamestrike both the minion wave and him shows that you must be playing at an MMR level where people are idiotic enough to stand inside their minion waves vs. characters with circle AoE's (KT, Jaina, Tass etc). Any non-shit player will force you to either burn your AoE on the wave, which means you can't use it on trades, or use it for trades which means you lose your waveclear ability.
Yes, when a Sonya is walking towards you their intent clearly isn't to spear onto you. It's so not telegraphed.
Maybe because in noteworthy MMR level games you always have a bunch of heroes roaming around and going to the enemy's side of the lane without seeing all 5 enemies on the map is a death sentence.