It's no revelation that Squishies die from anything. Shyv only needs a damage item or two before she starts building tanky, like you'd see if you looked up her builds. She can be DPS and Tanky at the same time, since she's tanky enough to not die from anything, but enough damage to kill squishies, with items like Titanic, BorK, and Triforce, backed with Tank Items.
How am i focusing Azir? I brought him up once saying he needs to put his life on the line to Shurima Shuffle. And no, they're not applicable on Shyv. Gnar and Poppy are most certainly tanks, though in mini-form Gnar is more fighter like, since their abilites focus on DISRUPTING and CC'ing teams. Poppy has her wall to stop dashes, dash-slam, her Ult. Mega-Gnar has his W and R, meant to disrupt a team, and his jump to put himself into the fight, so he can cc fools.
Shyv is not applicable. Her ONLY cc is her ult, which is primarily a gap closer or an escape/meant to power up those abilities. When you think Shyvanna you do not think "Oh yeah, the champ whose primary purpose is to shove a team". No, you don't. Shyv is a fighter/juggernaut and like one, does not need to CC to back up her strong late game dueling.
And fixing the hitbox is a buff, not QoL. QoL is like adding the total damage a DoT ability has. (10 Damage a Sec/40 Damage total). "Fixing" a hitbox makes it more reliable is going to actually going to boost Shyv because she now traps enemies better, resulting in more kills, etc. A QoL doesn't bring people back into Meta, real buffs do.
Now, I'm not saying that Shyv doesn't deserve a buff or two, but you don't buff her into a classification she isn't. If she's struggling with dueling, buff her dueling, emphasize the strength instead of spreading it elsewhere.