Sion is extremely strong! Don't listen to the crowd!
Hi. Gold IV Sion main here to tell you that all these front page posts are from people that don't play him, or at least don't play him well. So what are Sion's main strengths and weaknesses?
Strengths 
(Blood is the wine of Victory)
• Very strong laning phase in most matchups, very safe in losing matchups such as riven or fiora
• Fairly easy to consistently land Q knockups in lane
• High base damage on Q and ult
• A properly timed W wins trades.
• Some of the best TP ganks in the game against certain bot lanes
• Very good at applying pressure to the map
• Strong early, mid, and late
• A TON of CC
• Uses gold very well, still very strong even if behind
• Does very well when paired with someone else with strong lockdown (
and 
are your best friends)
• Ult makes for some pretty crazy escapes
• Can do a camp/ steal an enemy buff level one better than almost anyone
• Is a surprisingly good duelist
Weaknesses 
(Only cowards fear death)
• It can be difficult to hit a team with all their dashes off CD • Every ability can be outplayed to some extent, although there are ways to circumvent this • Lowest base health of any champion level 1 • Passive is very weak to the point where it almost never matters after about 8 minutes into the game • If you mistime your ult, you are now in the center of the enemy team with no backup, similar to The Amumu Effect • Struggles against team comps featuring tons of CC • If your Q and ult are down you are now a lumbering hunk of meat with no way of getting close to people other than a paltry 40% slow
I can think of more if this post draws any attention. Just remember that just because someone says a champ/build/strategy/teamcomp is bad doesn't mean you have to believe them. Similarly, just because a champ is not played in the LCS doesn't mean it can't tear up solo que. It is your success that really matters. I was first drawn to Sion because I started watching Sickmotion's stream, who showed me how strong he could really be in the hands of someone who knew how to play him.
Sion is love, Sion is life.
