I think your argument would have been convincing coming from a neutral observer. But I’d like to address your belief that sanctions don’t work. You present it as a simple matter of “do work versus don’t work”. It’s always more complicated than you think. Sanctions always have some effect; however, that effect can be trivial or huge. It depends upon the circumstances. It’s silly to talk about whether they do or don’t work; it’s better to ask “How effective are these sanctions in this context?”
I agree that the latest round of sanctions make little sense. I believe that they’re just posturing that has little real economic impact (as you note) but reduces suspicions that Mr. Trump is indebted to Mr. Putin (which he indeed is).
The most important factor in the success of sanctions is the degree of global support they attain. The sanctions against North Korea that Mr. Obama orchestrated were fairly effective because even China and Russia grudgingly participated. Much the same can be said about the sanctions against Iran. However, it takes only one major country to ruin the effectiveness of sanctions. Once Mr. Trump started his trade war with China, the Chinese opened the floodgates and goods poured into North Korea, gutting the sanctions regime.
Moreover, just as with military operations, you never get a clear victory. The sanctions against Iran did not succeed in getting it to abandon its nuclear program, but they did obtain a halt to progress towards nuclear weapons.
Russia has violated international law with its invasion and occupation of the Crimea and its attacks on Ukraine. It is appropriate — even necessary — for the international community to make it clear that established borders can only be adjusted by mutual agreement. For that reason, it is necessary to continue to levy sanctions of some form against Russia.