I think a good way for the Monk to go would be to incorporate the word's original meaning and classic/medieval flavor alongside/in addition to the "kung fu"/martial artist and shaolin/ki/spiritual powers stuff.
Then things like the shadow monk ninja, can be more properly laced into a Rogue magical assassin subclass. Elemental monks might be better served as sorcerer subclass or wujen style mystic, etc...
The [Steeldragons' for 5e] Monk
An ascetic (NOT "aesthetic", as mistakenly written by EGG in the 1e PHB and we've been paying for it ever since) and contemplative who meditates or prays, trains and studies for their own betterment and spiritual [if not also mental or physical] growth at a monastery devoted to a cause, deity or service. The character's origins might be a single sanctuary of personal enlightenment, a cloistered repository and archive of learning, secret/hidden place of spiritual or physical development, or a large system of connected facilities serving and/or spreading various orders within a religion.
Profs: No armor. Simple weapons
HD: d8
Tools: 1 set of artisans tools or 1 musical instrument.
Skills: Select three: Acrobatics, Athletics, History, Insight, Medicine, Persuasion, Religion, Nature, Stealth
Saves: Wisdom and one determined by your subclass.
Base Class:1st: Unarmored Defense, Unarmored Movement (+10' only, without armor or shield)
2nd: Spirit Points (work like Ki/Sorcery, etc...), Defensive Action (bonus action to Dash, Dodge, Disengage)
3rd: Monastic Tradition: Cloistered Clergy, Martial Adept, Sacred Disciple
4th: ASI, Divine Sense (as 1st level Paladin feature)
5th: Stunning Strike, Extra Attack
6th:
Tradition feature, Uncanny Dodge
7th: Stillness of Mind, Wholeness of Body
8th: ASI
9th

urity of Body
10th: Tranquility
11th:
Tradition feature
12th: ASI
13th: Evasion
14th: Diamond Soul
15th: Timeless Body
16th: ASI
17th:
Tradition feature
18th: Astral Projection
19th: ASI
20th: Perfect Self
Cloistered Clergy
3rd: Bonus Proficiencies: Intelligence saves, Shields, 1 additional Wis- or Int-based skill of your choice; Aura of Protection (as 6th level Paladin ability, only to 10', use Wis. mod.)
6th: Sneak Attack (as 1st level Rogue feature)
11th: Aura of Courage (as the 10th level Paladin ability)
17th: Channel Divinity: Turn Undead
Martial Adept
3rd: Bonus Profs: Dexterity saves, Light armor, 1 Martial Weapon of choice; Martial Artist: spend Points: Flurry of Blows, Deflect Missiles, Slow Fall
6th: "Ki-Strike" (spend points for special "magic hands" extra damage)
11th: Improved Unarmored Movement (vertical and over liquids)
17th: Quivering Palm
Sacred Disciple
3rd: Bonus Prof: Charisma saves, 2 additional Wisdom or Charisma based skills of your choice; Spellcasting: spend Spirit Points to use magic, 1/3rd caster progression & spells known (as the Eldritch Knight), Wisdom casting ability, choose from cleric and/or druid spells.
6th: Divine Strike (as the 8th level cleric feature)
17th: Transcendent Spirit (spend Spirit points to teleport or dimension door?)