I have been pondering this for a long while now how to enhance the mage tree as it seems to me to not be very magical.  While I was thinking I came up with a potential idea.  The general gist is make a trait line that gives a magic research bonus which replaces the spell mastery line and unlocks 4 spells per tier with 4 tiers.

Each spell tier would allow for the self caster to upgrade a magic trait while casting the spell would cost you gold and mana.  To make this a non abusive trait bonus you could make the costs 100 gold and 200 mana for the tier 2 trait research, 200 gold and 400 mana for the third trait tier and so on and so on.  This  requires you to have the initial trait, which makes the Decalon more useful.  This allows for more magic in the mage tree while not making this bonus not too overpowered.

Lastlysince mages have access to more spell traits, even if not easier to get the summoning line should be reflected by making it work like others, and myself have suggested like so;

Summon I => Attunement I => Summon II => Attunement II => Summon III => Elemental Attunement (Mage acts as an elemental shard once they have tier 5 of their respective spell tree and this trait, if maxed out a mage would act as all four elements).

Anyhow that's my suggestion, thanks for listening.