First: Is it correct to assume that in normal conditions you should run away from any company with shady liquidation preferences?
I've been in a few "high quality" startups, and in most cases if the company was liquidated for a price larger or equal than the last valuation, essentially the preferred shares would convert to common, since the preferred status didn't give any advantage to them from that point on.
If the company sells for less than the last valuation then yes, common holders will be progressively wiped out since investors (preferred shareholders) need to recoup the money they invested, but at that point you really just placed a bet on the wrong startup, nobody has been "screwed".
Second: on strike price, from what I've personally seen one "advantage" of common options is that the strike price is usually a fraction of the actual preferred share price (let's say from 1/10th up to 1/3rd) so, even if the company valuation doesn't increase much, the employee can still gain some benefits (and this is assuming that my first consideration holds, since if there are aggressive liquidation preferences you're going to be screwed, and that there won't be too many dilutions down the road).
Mind to share your opinion? You seem very knowleadgeable