The first thing you have to consider is that apart from being a game it is a commercial venture, and commercial ventures are designed to separate people from their money.
Secondly it also a trap.
Third,by design or accident there is an inbuilt obsolescence.
The latter may not be immediately obvious to those who haven't been playing long.
Now to the consideration of Inga.
She was the second shaman to Baggi,apart from other extras, both had a specfic purpose to them, aiding knowledge and building.
So you start spending on these two shaman, then along come the others to assist with scouting and attack of the various kinds of troops, so you start spending on one or more of these..
Then much later along comes Raine with the realization that apart from better building and knowledge bonuses , Raine offers something else of importance so, is it best to start again from scratch or finish off Inga and Baggi and your troop type shaman?
Sometimes your basic shaman is going to be more useful, because it's at a higher level than Raine, which is most useful for its extras connected with siege.
Slow players who havent rushed to buy everything as soon as it comes out have some advantage over those that did, as do new players by coming late to the party.