To be entirely fair, only a handful of those probes had the equipment to detect life directly, and none had the ability to search for life in all possible environments for its existence.
Not that the planets in our solar system are particularly good places to search for life, but that is no excuse for Alpha Centauri Bb- it is probably a worse environment to search for life than pretty much any planet in our solar system.
In terms of 'alien ruins', of course we haven't found any of those (unless you ask conspiracy theorists). But you did say 'alien life', and of course, alien life can exist without leaving artificial structures... and artificial structures can exist in lifeless environments.
IC fusion is the most promising method of interstellar propulsion. Antimatter is pure science fiction at this point; even if you could produce the quantities needed for interstellar travel, figuring out how to contain it within a spacecraft and 'burn' it usefully is another matter.
Various forms of nuclear fission propulsion may be easier to develop, but do yield lesser performance.
Longshot does seem rather more conservative than Daedalus; for example, it uses an onboard fission reactor to power the IC lasers, whereas Daedalus used power from the fusion reaction itself to power the lasers. It also has a far lower mass; a wet mass of around 400 tons (comparable to that of the ISS, an actual assembled structure in space) compared to Daedalus' initial mass of over 50 000 tons. Daedalus was an absolute beast, even setting aside all other technical issues it'd be implausible to field in the near-term simply due to its prohibitive size.
