Your observation doesn't contradict the point of the comic. It isn't about which tasks are difficult in totality, it is talking about which tasks are difficult with our current technology.
The idea is that non-software developers don't know which tasks current technology can solve trivially and which tasks can't be. Yes, the distribution of those tasks into the two buckets changes over time, but it is still not easily knowable by lay-people.
Everything we do today would be extremely difficult to re-create from scratch, but that doesn't mean it is hard to do - because we DON'T have to re-create it from scratch.
The idea is that non-software developers don't know which tasks current technology can solve trivially and which tasks can't be. Yes, the distribution of those tasks into the two buckets changes over time, but it is still not easily knowable by lay-people.
Everything we do today would be extremely difficult to re-create from scratch, but that doesn't mean it is hard to do - because we DON'T have to re-create it from scratch.