So much misinformation here:

However, there is a 100% yearly inflation. Assuming the market cap remains constant, that means each STEEM will lose half of its value by next year.

No, 90% of that inflation goes back to Steem Power holders

There is also another risk: even if you buy STEEM and power them up, you might end up losing more money to inflation than you will make from contributing on steemit

Same answer as above.

My suggestions: Actually read the whitepaper! It covers all this stuff!