Luden's echo is overtuned
Mage itemisation was reworked back then because of how the old 
was overshadowing every single other options that the AP itemisation had to offer. Immediatly after the rework, 
was king only to get nerfed back to being an option mainly only for mages who NEED an huge mana pool. Meanwhile, Ludens Echo, a single item that has been ignored for so long gives:
1- The 3rd highest amount of pure AP amongst every base finished items
2- The 2nd highest amount of mana amongst every base finished items
3- 20% CDR (!!!!!)
4- Additional SCALING burst "AoE" damage
5- The possibility to proc any single "On spell hit" effects in the game with its active, including every applicable keystones, every applicable runes and items passives like 
and
6- An easy build path that includes 
, who gives virtually unlimited mana for the laning phase.
offer way too much raw stats and is way too easy to build as a first item. At least, before, it didn't give mana so rushing it was kinda suicide for most mages. And now, with runes and keystones becoming stronger and stronger, its effect can proc waaaaaay too much damage that can't be dodged if you are anywhere near the impact, be it ally champion or lane minion, even if you miss your skillshot. It should either bring less raw utility and stats or synergize less with on-spell-hits effects.
