Don't forget you do want one limb stiffer than the other at the end. The bottom limb should be slightly stiff because of the way it's actually shot as compared to how it's held on a tiller.
Are you pulling the string from the middle and supporting the bow in the middle? If you are, leave one limb stiff and draw the bow in front of a mirror (or get somebody to draw it while you watch) and you'll be surprised how different it looks. It will come round nicely in the hand if it's slightly stiff now.
If you've accounted for this, and you're pulling the string say an inch above center and supporting the bow slightly below center then you do want to be going for an even bend on the tiller tree, but it's still incredibly hard to emulate a real draw on a tiller.
It.probably isn't the woods "fault" per se - all wood is different and as a result it all throws up different challenges every time. There's no such thing as a perfect stave - the next one might not have as obvious density issues, but instead might have grain run out, hidden rot, knots, pins, spalting, twist, deflex..... And so on. You just gotta go with it each time and beat it. For what it's worth though, there's no reason not to splice your next one - a few really talented bowyers have made super heavy warbows (160# plus) that bend full compass despite being spliced.
