i dont understand why yall are even wondering if you need this to get up death mountain every time ive ever scaled it ive had no problems i walk right up... are yall playing a diffrent version or something?
After you beat Dodongo's Cavern, bomb the rocks on Death Mountain Trail and walk down the path to get to the Great Fairy that gives you Din's Fire, the volcano erupts and spits flaming rocks at you, no?
If anybody was curious, I finished the run! 38 deaths in all, which is pretty disappointing. Lots of these were incredibly stupid deaths down to experimentation and forgetting how to fight things like Stalfos. I bet I could get down to <10 deaths if I tried again but it's too soon to be playing OoT again. Next year, maybe.
Regarding Ganon's Castle: the longshot on the Like-Like trick definitely works, although it's not very lenient (it's not difficult, you just have to make sure you're right on the edge of the platform) so for a good while I didn't think it was possible. During this time, I discovered that it is also possible to instead use the Hover Boots. From the torch, back-walk towards the temporary platform closest to the Like-Like and at the end of the hover back-flip (timing's a little tricky) and that will get you far enough to land on the platform. This isn't easy because you have to spend the entire time L/Z-Targeting with the camera towards the torch so you can't see the platform at all, and if you do land on the platform you have to react fast because you'll have the momentum from the Hover Boots and the camera will still be in the wrong direction, but it's definitely possible.
There's two other places that 'require' Fire Arrows in Ganon's Castle: the Forest Trial, which is pretty obvious to get past; and the Spirit Trial. There's a cobweb on the ceiling that doesn't react to Din's Fire, and it can look impossible without the Fire Arrows. However, it's possible to fire an arrow from the torch earlier in the room to the cobweb, but it's a very awkward shot. Definitely possible.
On the topic of the Spirit Trial: even though you can beat the Spirit Temple without the Bombchus, there's a part in the Spirit Trial that, as far as I can tell, definitely requires the bombchus. Nothing else I tried seem to reach the switch. Bit of a shame, but oh well.