Advanced arrows are not pointless. Some have dual damage (like fire arrows). Others deal only pierce damage, and every single damage point in difference may be the one that allows you to one shot this monster, or not. Given that any surprise attack grants an immunity of 5 minutes, sometime, a single point less means that one, two, three arrows are not enough, that the monster is running toward you on top of others, and you are not prepared, etc.

On the other hand, arrows may be costly.

As for skills, I think that you died several times in a row (that's easy to do).
On each death:

1. all skill progress bars are reset: all skills are set at 0 XP in current skil level.
   
2. 5% of skill levels are lost in each skill. This equates up to 5 levels at level 100. The loss leads to a fractional level, that is; new level plus some progress on the skill bar.

For examples, and also the effects of being skilled, you can look at this:
https://guidescroll.com/2021/03/valheim-skills-xp-and-combat-guide/