Um mago invisível mantendo outra concentrada - quão ruim pode ser isso? 
Fora isso, só acho que tecnicamente não seria 'arcane mastery', mas um tipo de 'signature spell', mas isso já é preciosismo meu.

No geral parece mais original  e equilibrado, embora pareça propenso a risco esse lance de concentrar em duas magias por vez, embora, com os limites atuais, não tão fora da curva.

Pessoalmente, vendo bardo, eldricht knight e arcane trickster poder pegar magia de qualquer classe e o supremo estudioso do mago não, eu não veria problema do loremaster poder aprender magia de qualquer classe com uma feature de lv6 - ainda com alguma restrição, sendo em alguns níveis específicos ou apenas uma de cada círculo de magia... mas sei que isso é especialmente e essencialmente para proibir o mago de ter magia de cura por pura vaca-sagradisse, já que não há nenhuma eficiência embutida nisso.
Escolher ser apenas de ritual parece ser um limitador justo.

Verdade. Confundi no caso dos half-casters, mas ainda estava certo sobre o bardo e mantenho o que disse.

Vamos ver se o elfo aparece e comenta

Embora, como demonstrado recentemente, a ideia de Wizards e Sorcerers não terem magias de cura em seus repertórios é tb uma questão dos grognards.

Ritual Master
Beginning at 6th level, you can inscribe spells that have the ritual tag from any class’s spell list in your Spellbook. For each level of the spell, the transcription process takes 2 hours and costs 50 gp for the rare inks needed to inscribe it.

Arcane Mastery
At 14th level, you have achieved such mastery over certain Spells that you can maintain concentration of them together with other spells. Choose a 1st-level wizard spell and a 2nd-level wizard spell that are in your Spellbook and requires Concentration. You can cast either of those Spells at its lowest level and still cast a second spell that requires Concentration. If you fail a Concentration check while concentrating on two spells, you lose both spells.

2nd level feature
Magic Savant
Your investigations allows you to go deeper in the arcana knowledge than other wizards. Beginning at 2nd level, each time you gain a wizard level, you can add three wizard spells of your choice to your spellbook for free, rather than two as per standard rules. Each of these spells must be of a level for which you have spell slots, as shown on the Wizard table.

In addition, you can inscribe spells that have the ritual tag from any class’s spell list in your Spellbook. For each level of the spell, the transcription process takes 2 hours and costs 50 gp for the rare inks needed to inscribe it.
 

6th level feature
Font of Knowledge
Beginning at 6th level, you become proficient in your choice of two of the following skills: Arcana, History, Investigation, Nature, or Religion. You can learn a language instead of becoming proficient in one of these skills.

In addition, you add the Identify spell to your spellbook if it is not there already. When you cast the Identify spell you regain one expended spell slot of 1st level. At 9th level, you add the Legend Lore spell to your spellbook if it is not there already. When you cast the Legend Lore spell you regain one expended spell slot of 5th level or lower.


10th level feature
Prodigious Memory
At 10th level, you have attained a greater mastery of spell preparation. As a bonus action, you can replace one spell you have prepared with another spell from your spellbook. You can’t use this feature again until you finish a short or long rest.


14th level feature
Arcane Mastery
At 14th level, you have achieved such mastery over certain Spells that you can maintain concentration of them together with other spells. Choose a 1st-level wizard spell and a 2nd-level wizard spell that are in your Spellbook and requires Concentration. You can cast either of those Spells at its lowest level and still cast a second spell that requires Concentration. If you fail a Concentration check while concentrating on two spells, you lose both spells.