I’ve never encountered straggling pieces with spruce wood so idk

He must be chopping like Acacia or smth that's broken up. A quick fix would be to just redefine what a tree is: any logs that are adjacent or diagonal to the block are considered part of the tree. Whereas now I believe it is something like any logs that are adjacent to the blocks are considered part of the tree. It's probably more complex than that but if that is a common issue, I'm sure it can be fixed. (maybe)

nah orange, i chop spruce by the bulk, often resulting in pieces on top

I never had this issue, but there is a definite limit to how much it will chop. As well, netherite axes last longer in my experience. Perhaps you're drawing the short stick.

often times i found straggling pieces on the top, hindering my ability to make a solid block of tree

There are definitely straggling pieces on the top, maybe just increase the limit by 10-20 blocks then it won't be op for griefing or smth but will still definitely get the whole spruce tree. Also a much simpler solution.

Detect leaves by felling rune