i think riot has made it time to revamp mana champs and/or items
pre-season patch changed a lot about the game and it feels like several of these changes have come together to weaken mana champs AND make the mana game more boring than it already was.
in reference to their power: mana regen items were nerfed in the early game, when mana management is the biggest issue chalice of harmony specifically was nerfed to keep it from being the only real option for mana champs who aren't stomping their lane blue buff's duration was reduced in addition to making the jungle much tougher, so a mana jungler will be much less likely to donate blue buff to a laner, and if they did it would be less impactful
in reference to the depth of mana management: the chalice of harmony still regenerates more mana when you are low, but it does it by recovering %missing mana instead of increasing your regeneration by the % of your missing mana. this means that chalice favors large mana pools and building bigger pools where before it favored large amounts of regen and building more regen. this means it falls into the same niche as catalyst and tear of being for champions who like large mana pools. if you're playing a mana champion that wants to cast their spells in a big combo and need a huge chunk of mana, you now have another great option because chalice will synergize with your large mana pool, but if you are a champion that spreads out the use of their spells over a long period of time, now all of your options are kinda crappy and don't really fit with your spell casting model.
I think riot needs to take a look at mana users right now and try to figure out what it means to have mana vs. only being restricted by cooldowns (don't compare it to energy or health cost champions because they aren't really used well on either of those classes). give mana users either abilities or items that let them go from conserving mana to efficiently using mana to dumping mana throughout the lane phase and later on in team fights as fits the situation, make building mana or mana regeneration worthwhile without easily hitting that threshold where you can just cast whatever you want whenever you want, and make more options than just salvaging a bad lane (chalice into whatever) vs. wait for lategame (catalyst into rod) vs. SUPER wait for lategame (tear into whatever)
perhaps riot should look into making a passive similar to archangel's that's available for champs that aren't great at stacking tear, maybe that should be the way to get a big AP powerspike instead of the current and IMO boring rabadon's riot recently gave cassiopeia a very powerful form of mana refunding on cs like a dring on steroids that players find fun, maybe dring could be increased in power while still allowing for healthy laning maybe there could be an item that creates windows where mana costs are dramatically reduced to allow a champ to just start slinging spells to quickly clear a wave or nuke something without worrying about what it will do to their mana pool (contrariwise this means they would be more vulnerable when this window has closed because they don't want to cast too many spells and kill their pool before the next window opens up) what about an item that lets you dump extra mana into spells to increase their damage or effect? (or even add a new effect?) there are a lot of implications for this whether the dump is made efficient or inefficient
The default status for a champion is a mana user, but this just makes your champion feel like it's an antiquated design when you stand it next to a manaless champ and can't find what they had to give up to not need to manage their mana or what you gain by building blue crystals that do nothing but let you use your abilities.
