I think the tree is fine (Overall as an idea and Concept), and I can imagine that it plays well too while leaving interesting choices playstylewise, too.
I feel, for myself, and maybe also for other People, that the general theme of the mage as he finds himself now with the skills currently available, is that you have mostly “shoot” skills that lack diversity in the way they are played (as skills and therefor as how the mage plays itself).
That leaves less room for the mage to be a mage. To also be tactical in more adverse ways that highly differentiate from each other. Right now, the mage feels - despite the many skill choices (in regards to damaging skills like fireball, Meteor, orb, etc) - that there`s not much choice in playstyle other than differentiating melee with spell. So either you go melee, or you cast. But you cast damage, and for me most damage skills feel the same the way they are cast and played out: Cast, deal dmg, cast again. Positioning, Timing ain´t important. Its mainly: dish out damage.
The only skill that feels more tactical and changes the Gameplay dynamic a bit, for me, is the orb - for it can be prolonged via decreasing its Speed, therefor it being a longer-lasting Duration-spell skill that is dealing damage over a few seconds (without being a “DoT”).
Spells that deal Damage over a period of time (not necasserily “DoT”) - but something like… a firestorm, a hurricane, a Blizzard, a Lightning-storm in a targed area, that deals its Damage in X seconds. A stationary Hydra, a thunderstorm that strucks enemys in the Cloud, or something.
A “click-and-Forget” and “use-other-abilites-too-during-its-duration”.
I love mage for being a kiter, or having a feel of the kiter! Black-hole comes closest to that, although it is very different in its concept and purpose of usage - its mainly crowd control and high CD, which is fine - but thats not what I`m pointing at.
For me, right now it feels bland because all his abilities - albeit being different - “feel” like the same, as in, there`s not much choice… the only choice is, “with what will I deal Damage with”, but not “how will I deal Damage differently and therefor play my mage differently”. Which skills i will use will not alter my game-Play much, because the differentiation between the skills is more a matter of “how much dmg and mana does it cost”, but not necasserily “how will it make me play my mage differently in the way I deal my damage and survive”. For it plays differently in the sense that there´s another visual skill coming from my mage when I press that button, yes, but not to the degree that makes it interesting and fun as in, I have to play and move my mage differentl, not in the sense that gameplay-Dynamics really change.
Other classes do this quite well, IMO. They feel diverse with each of their dmg-skill-choices, because they all more or less allow for different game-play and do different things that matter. Mage mainly does damage, so there`s not as much choice involved, other than Maybe being Ultra fast and efficient (cast Speed, dmg, mana reg).
E.g., lets say we have a thunderstorm skill that Costs 60-80 mana or something and lasts 4 seconds, dealing moderate amount of Damage in an AoE over its duration. It`s not meant as a crowd-control like black-hole is; its mana cost are expensive, because it actually is a strong damage-dealing-skill. It IS meant to be played around, so its cooldown is shorther than its duration.
I could think of many skills like that that would have good Synergy with current skills in the game, making for a looot more viable and different builds and playstyle-combinations than there are atm (in my opinion) for the mage. Disentigrate does a good Addition to that I feel, since it offers alternative mechanics (quite the opposite of the above, which is: stand still and deal damage over time (which isnt DoT)).
E.g. Any type of Elemental-Hydra - medium mana cost (35), long Duration (6-7s), Shorter cooldown (2-3s), medium damage Overall (can have multiple on the field, 2 or 3 total), stackable in damage with medium range
Any type of storm (firestorm, Blizzard (Cold), lightningstorm) - high mana cost (60-70), medium Duration (4s) and cooldown (3s), non-stackable in damage, high AoE
Some other Kind of this, like a Hail, or a fire-eruption, middle-high in mana cost (45), middle in Duration (5-6 seconds) and low in CD (2-3s), stackable in damage with medium range and damage-output
Its stationary and viable as a damage-skill, and it can be combined effectively with all the “spam” spells that youve got - fireball, Meteor, orb, etc. Glacier and meteor too feel more like a fireball skill than it does like this “stationary-duration-based” skill, therefor being on the same tactical-skill-choice-chart as the other “cast-and-hit” skills essentially (except melee-mage-skills and the defensive ones ofc, they of course do alter play-style wise^^)
I`d wish for more variety in active damage-spells playstyle-wise. Disentigrate does a good Job with this! I think in that regard, we Need no more “shoot” skills (which I see Meteor and glacier also being such), and more like this (disentigrate offering different mechanicsplaystyle-wise).
Elemental nova does a good Job in adding to the variety, although its not my favourite skill on its own and its not ranged-and-kite-ish, but it adds to the way a caster could be played, it combines good with a melee based mage because it profits from being up-close, and is nice with spells that make you less mobile, therefor “force” you to be more up-close at least sometimes - like disentigrate, therefor adding interesting Juices to your play-style-possibilities.