This is about future cash v P&L.
From a P&L point of view, with an expensive capital asset, you need to work it hard to get the healthy returns because of the high depreciation hitting the P&L.
From a cash point of view, once you’ve spent the money it makes no future cash difference whether you use an old or new plane.
So, both of the above posts are right, but one is arguing on future cash outflows (no difference), one is arguing on the health of the P&L (it does make a difference).