Same as it used to be.
Every tree has different ~yield.
Even high tier trees have different yields depending which one you chop down.

For example I used to go for wood until my inventory is full and my steel axe would lose just over half of its durability. Now knowing the exact trees I am after which gives me exact same full inventory, my axe only loses ~1/3 of its durability as I only chop down high yield trees of about ~100 sapwood and ~50 heartwood per tree.

Okay, so within a tier each tree returns a specific (but varied) number of heartwood?

Damn this game seems to manipulate the grind in a truly and obviously a mystery through obscurity fashion. My interest has waned significantly as the mystery transforms into obstinate time sinks.. sorry for the negativity, and thank you for your time answering the question

Each type* of trees within its own type/category.

Yea I like to chop Oak trees (rough bark) in the forest...the large ones give 50sh heartwood with 100 sapwood per tree...thinner oaks give 30sh heartwood and 60sh sapwood...just ignore all the birch trees regardless of their size,,,they do not drop much heartwood. Takes me like 15 mins to get a full load and helps great making charcoal. This is with Max Woodcutting at like 41 and T2 Axe...will go quicker once I can make the steel axe.