so from what i can tell going over this, Tanjiro has the agility, skill and intelligence on lock, his weapon also nullifies the troll's most major feature, their regeneration. This all are pretty good advantages, where as the troll is significantly stronger both in LS and AP, it's durability is also going to be an issue aside from it's regeneration, Tanjiro's sword is going to have a hard time doing meaningful damage to the troll initially, as it's 3x more durable, is basically too dumb to feel pain AND has damage reduction, along side this, while Trolls are about as dumb as they come, they WILL retaliate against threats. His size and natural range also is a pretty big advantage to keep Tanjiro away as it's literally someone fighting against a person who is wielding a weapon longer and bigger than them, held by an arm that's longer than they are tall and that's not including their vomit.
There are several key threats that Tanjiro has to get around here
1. Avoiding getting grabbed, if he gets grabbed once, it's over for him (LS class 50 vs Class M)
2. Avoiding getting hit by raw Dhar which will just annihilate Tanjiro instantly.
3. Avoiding Acid Vomit, which will instantly melt through Tanjiro and his Nichin blade (there is also the threat of having to avoid damaging it's stomach at all as that will also releases the acid and destroy his sword and him etc.)
4. Avoiding causing too much damage to the Chaos Troll as it's Reactive Evolution is basically on steroids compared to other Trolls, will extra limbs, heads, spikes and other stuff just bursting from it when it gets hurt, which only make it harder for Tanjiro to fight with each non-death blow he deals.
5. Avoiding getting Eaten.
6. Avoiding just straight up getting cleaved or crushed or beaten considering the AP difference.