You're comparing apples with oranges there.
Tippa is a forward, and not expected to get to contest after contest. He is however expected to run and chase and provide options for 4 qtrs, which I think he has done all year. I suspect people assume he doesn't have a big tank but he actually does.
Parish is a good comparison to Zach - Parish can't run out a full 4 quarter game yet, and generally fades after 3 qtr time.