Fandral shouldn't have planted it without the aspects blessing in the first place. And rather people lived there or not isn't relevant on rather the Haranir are happy about it being planted and cut down. I'm not comparing the two tree cutting events on being a warcrime cuz one is obviously worse.

Also Fandral Staghelm did make Andrassil which then had to be cutdown. I can't imagine the Haranir were too happy with that.
Both factions are responsible for the destruction of a world tree. Teldrassil was just more dramatic.

Saaaaaaaaaaaaaaame

sidenote: generally I'm of the opinion it's better to find a system that fits what you want rather then to rig up another system for that. We wanted to play a pokémon adventure like the games but tabletop. It's also just healthy to diversify how many systems you've experienced for ttrpg's.

We used the PTU system. It's... not perfect. We did do a bit of tweaking it. For running a pokémon campaign where your players are the trainers its from the systems I found the best (though thats 3 years ago). It's build for that so even if the system was flawed it was the best choice.

I don't know if there is a way to make you feel better right now. But you're not alone. I would advise not trying to go through this alone, stuck in your own head.