To your point (3), perhaps it is reasonable to bring a lifetime's supply of vitamin supplements for four people. But with an artificial lamp you would have to worry about bulbs burning out (how many would you need?), and the lamps would consume a significant part of what would have to be a limited power supply in the colony.
To your point (4), that there may exist an even more difficult problem does not mean that building a Mars vehicle is "not especially technically challenging." The author explicitly cites the three recent malfunctions with rocket launches, and the older Apollo, Soyuz, and Shuttle programs all had their difficulties too. Building a Mars vehicle is surely challenging.
You wouldn't build such a lamp like on Earth. An oxygen plasma with a spectrum filtered glass case, microwave excited to avoid the need for electrodes, would last pretty much forever and be repairable using only in with materials.
To your point (4), that there may exist an even more difficult problem does not mean that building a Mars vehicle is "not especially technically challenging." The author explicitly cites the three recent malfunctions with rocket launches, and the older Apollo, Soyuz, and Shuttle programs all had their difficulties too. Building a Mars vehicle is surely challenging.