would you not conclude that the probability of solving these less ambitious problems is much higher ?

Honestly, the error bars on all of these expected-value calculations are so wide for me that they pretty much overlap. Especially when I consider that building a run-of-the-mill marginally-superhuman non-quasi-godlike AI significantly changes my expected value of all kinds of research projects, and that cheap plentiful energy changes my expected value of AI projects, and etc., so half of them include one another as factors anyway.

So, really? I haven't a clue.