clearly you're going to be getting reported like singed smite support or nunu smite support, and I assume eventually going to get manually reviewed, but if you get reported just a few times would it be bannable to get manamune and archangels on someone like 
Hethalean1 votesI like the comparison because after a lengthy review process Riot decided that Smite Supports on Singed and Nunu was not punishable if you're playing to win. You can get reported for anything in LoL (just like you can get sued for literally anything in real life if someone wants to waste their money...) doesn't mean that anything'll happen though.
MYSTlCFLOW1 votesohh didn't know they came to a consensus and said that they won't be banning players like that that are planning to win. well that's good cause I know singed was threatened with a perma if he kept it up and I think the nunu smite took place after singed's case, so It's good they finally decided, but like.. XD I'm pretty sure it's pretty objective that if a gets a archangels or manamune that he's not trying/trying with a fair degree, to win the game, I mean those items cost a lot.. and the main purpose is the mana it gives. I'd be scared if i fell below 50% winrate
Hethalean1 votesYou can screw around with your build and not be trolloling. Look at Renekton. He EXCELS with Essence Reaver, but has 0 mana. Therefore, he has 0 benefit of part of its build path nor it's one passive. I'm not sure with Archangels and Manamune. However, it could be just someone inexperienced not knowing exactly what to do with Zac (and deciding to build AP and those items since he's some mid main who likes champs that happen to build that or is an Ezreal main). That's the fundamental issue. Is the person I'm doing with just inexperienced at this champ or is he trolling the team?
MagicFlyingLlama1 votesIf you are not otherwise trolling, no. It is very sub-optimal, but it can have a purpose.
Hethalean1 votesRiot doesn't ban for suboptimal... How could they? That changes so often, right!?
MagicFlyingLlama1 votesRiot doesn't ban for suboptimal... How could they? That changes so often, right!?
They ban for excessive trolling with suboptimal builds, but not suboptimal by itself.
Hethalean1 votesYeah, agreed. Suboptimal is an opinion based comparison. What is optimal? What is too suboptimal? Builds vary. Riot themselves have an idea what they think works for a champ and has been wrong before often in the past.
Then you can just say "Have the system go by what is most frequently built". That has flaws as well. Look at Banner of Command... Saw ZERO play and it's incarnation was completely unchanged for the longest time until it was simply mentioned in Patch Notes about "Yes this applies to Baron buff and BoC" then it was super meta quickly. It's really hard to judge because 'optimal' really means meta, and meta is based on how people feel about a champion and what they think is good.
MrFawknSunshine1 votesi see no reason to get either but if you wanna put urself in a worst position to win well no one can stop you
Lotus Bloom1 votesConsidering that manaless champions cannot stack Tear of the Goddess, or Archangel's Staff it should be considered trolling. Is it a punishable offense? Who knows, gotta ask yourself if you think they were unaware, or if they are still playing to win. As previously mentioned by others if they are still playing to win then odds are that it's not going to be punished.
As the effects of these items are the main reason they purchased Riot could, and probably should, just set up the items to where they are unbuyable by manaless champions, however I find this highly unlikely to ever occur.
-- Snippets from the League of Legends Wikia --
"MANA CHARGE on Tear of the Goddess and Archangel's Staff requires mana expenditure in order to charge, making it impossible for manaless to charge either of those. On Manamune, on the other hand, manaless champions can charge the mana through basic attacks, until it upgrades to Muramana."
"On manaless champions, the AWE passive will have no effect whatsoever, and Muramana's SHOCK will apply but deal no damage."