yeah not to worried all in all as i have my ME1 and ME2 saves my only complaint is the default story is truly the ultimate move done each time at the end of the story. really does annoy me they dont just use the msot popular options of the players who from my searches showed paragon ending for ME2 as most popular choice.
really happy by default wrex is alive in the demo though. love him so much more than grunt
lol i learnt same thing early also. luckily i went soldier first cause i was off myth omniblade was a soldier only perk but as you said part soldier builds will have omni, tech will use electric omni tool and biotics will use a hadoken blast like miranda did in ME2.
not sure how they picked what to use with cross classes prob whatever looked cool and was needed to balance it out evenly