Ah yes, thx for asking all the important questions. But for the most part of what I have seen, extreme characters are only fit if you are in a gud team.

Extreme characters have high potential if used with a great team or against stupid opponents. I own a couple extreme character and started to notice that my winrate is dependant on a good team comp that isn't just full of a bunch of twats who play popular characters even tho the spot is filled. If your teammate is decent(coordination or composition wise), you can be great asset that can heavy carry or heavy carry assist. The same can be applied to extreme characters if the other team has bad team comp or bad coordination.

Always stick to a 2-3 team if using or assisting an extreme character is what I usually do. Easy and normal characters are relatively easy to understand and have a large error tolerance that one mistake can usually be covered. Unlike hard to extreme who take some practice and have very little error tolerance and are usually very strong in one aspect but weak in other as easy and normal tend to be all rounders.

I am entirely sure that if a team that had about 2-3 experienced extreme character players against 2-3 experienced normal character players, extreme can easily control the game. But I could be wrong since I have yet to see more than 2 extreme characters on a team. Easy to normal have higher curves and there are rare cases where hard and extreme can also have high curves as well.

Overall it is mostly dependant on a team so try not to solo que or take command and tell everyone what to do at certain times. I've done that when we seemed to be losing early game so I wanted to stop them from rolling through the team.

Ideal team and shiki plays: -tell them to never over extend when they are feeding. -Stay in groups: 2 groups of one with 2 and another with 3, a group of 4 pushing and harassing enemy and potentially getting a tower while 1 other destroys towers, or just a whole team of 5 with everyone doing their respective parts: tank assisted by 2-3 shikis while 1-2 (marksman, mage or ninja takes the sides and back to take care of the enemy marksman and mages. Literally this is a tactic in majong/chess mode. -during orochi waves, stick close to base and defend towers from minions. In fact at all times, minions should always be prioritized rather than shikis while being pushed. -Play tower if your shiki isnt suited against the opposing shiki meaning fall back for the tower to be a sheild and an support while you prioritze minions to not get steam rolled. -Burst characters should usually ambush then retreat to weaken opposing shikis. -While minions are within range of opposing tower whule you have a burst or charge character. Hit n run the shiki. -when opponent uses pesky skill you then use yours to counter them.

Of course these are all very unlikely to see from a player and even less likely from a team which is why just high dmg output/control teams are always going to be better.