I’ve already posted my thoughts that limit per skill may be increased. It’s just not a good time now for doing so.
But this words are more interesting …
So, if I’m understanding you correctly, let me rephrase this:
Some trees has low ratio of common node’s amount to amount of key nodes.
If that’s right, than I probably can agree in some cases. But still, it’s a balancing problem, I guess. Size of a tree itself can’t be a real problem. For example: Some time ago I’ve suggested Black Hole and Fire Shield reworks. Both suggested trees have their size about 80-100. But is this a real problem? Every suggested tree has 4-5 ways to advance, and the length of every way is 8-14 nodes with at 1-2 key nodes on it.
But lets return to “Summon skeleton” skill tree and other “large” ones. Yes, it may seem that they have to many common nodes and lack of key ones. But, in my opinion, it’s a problem of balancing and, sometimes, may require partial rework of problematic tree.