It took him ten hours of work the first time. Yes, it'll take him less the second time because he's gotten better at it, but it's still by no means easy or trivial. And we haven't gotten to how much he values his time yet.
Don't weight ten hours of learning about bicycle assembly as though it were ten billable hours if it isn't. Compare it against the ten hours you were going to do other things in: reading, watching TV, going out for a walk, whatever.
If I was the OP, I would do this exact thing: after putting some more miles on the bike and saving up that gas money, get a nicer bike and swap the motor. Better yet, sell this e bike for $2k now that it’s all upgraded and use that money for a full upgrade.