Everyone else has covered the more substantive issues, but on your point about lawyers - as far as I can tell, there is nothing close to a consensus amongst top startup attorneys that convertible notes are a bad idea.
Part of this is that good startup attorneys can help their clients avoid most of the issues you discuss - i.e. explaining what the terms mean, explaining that discount-only notes are relatively uncommon, explaining what happens when you raise an equity round at a valuation less than the valuation cap, adding in provisions to prevent liquidity preference double-dipping, etc.
Part of this is that good startup attorneys can help their clients avoid most of the issues you discuss - i.e. explaining what the terms mean, explaining that discount-only notes are relatively uncommon, explaining what happens when you raise an equity round at a valuation less than the valuation cap, adding in provisions to prevent liquidity preference double-dipping, etc.