When did I say "I" couldn't beat SA. I can beat both easy and normal solo, and with luck have beaten difficult in a team. But, I am the strongest player on my server (or one of the 3 of us who trade off #1 constantly). I use a setup similar to yours except that I use the water main's power scaling to be my heavy hitter. I would suspect that any decent player over level 80 could come up with a team to win normal as the scaling difference compared to level 90 is minimal. I am talking about the scaling for players below level 80. Remember SA unlocks at level 43.
All I am saying is Oasis needs to "look under the hood", and make sure that the enemies in the first and fourth round are properly scaling for newer players. If your server has level 85 players on it, then I wouldn't consider your server "new". And any friends on your server who might be lower leveled can have bonuses that might not reflect very high in their power number, but can impact this SA greatly.
It all comes down to a basic question of if you think "Easy" should be easy for all players and if you think it should be possible for the players who just unlocked it at level 43. In MY opinion, if this is a "bug" (and only Oasis can answer that), then it needs to be fixed. If it is not a bug, then Oasis needs to come out and say it is by design. If it is by design, then my argument would be that the attack levels for Easy should be reduced significantly and for normal minimally to make the game enjoyable for the AVERAGE player.
Special ninjas, strategy, and tricks make sense for beating difficult, but normal should be possible with just a good solid team and shouldn't require special ninjas, just a "normal" team. And "Easy" should be EASY, and anyone (no matter the level), should be able to beat it with 3 random ninjas that are fully leveled, cultivated, etc.
Actually, I think the real solution is give hidan SA for levels 43-64, hanzo for 65-74, yagura for 75-84, and itachi returns for 85-90.