Since it is porting to mobile there are several issues with drag and drop.
1. Lack of space
2. Gesture overload
3. Accessibility
I mean lack of space, in a cellphone the large menu with all characters is impossible. You cannot see, and cannot even properly drag and drop people in their intended spots. Even with a functioning drag and drop system.
Gesture overload: You know how cellphones allow you to enter a quick menu when you drag your finger through certain parts of the screen in certain directions? Yeah, that is one issue. The game would have to override that and it makes it confusing to users. However, the biggest issue is when you have drag and drop and you need to scroll down or up. There are small solutions but they are sometimes finicky and not always ideal.
Accessibility: Well some people do not have steady hands to put it mildly. Caused by a specific sickness or accident.
This goes into detail if you are interested:
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An alternative:
Discoverable controls: Basically have a menu with all the girls. When the user clicks on one girl you get the three options of placement. If the option is not available it does not appear. Similar to what was done in the labs when creating devices. You are never getting more than those 9 spots for any-one building anyway. If you want to know what is filled and what is not it is as simple as having a small bar with nine distinct spots that can fill themselves as you fill the spots. Does not even have to be a bar.
An example would be this:
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Now, if people still want something like a drag and drop here are some possible solutions. However, take note that these are for small screens thus they will look weird on computer screens and are not efficient.
Change screen: Basically give one screen with all options, then when an option is selected give another screen where they can drag and drop their choice. Like this:
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I understand why arrow clicking would become annoying but honestly, you could have just gone and look up why drag and drop is an issue, alternatives to the problem, and proposed solutions. I know the developer has to do this anyway and it would be basically doing the job for them. However, doing this shows two things, that you are not complaining and that you know of better ways of solving the problem. Some of them might be harder to code than others. Also, helping him explore avenues that he might not have thought of will accelerate the development process. Think about it, this is a group of no more than 5 people (from what I have gathered) developing a game. The quality is the same as an indie company with at least 10 people if not 20. Hence why it has taken a couple of years to finish. Helping them find better solutions will accelerate the transition.
Talking about the discoverable menu in the labs. I am not sure how well that is going to work on a phone. Mainly because it is a discoverable menu inside a discoverable menu to create a new mind controlling device. I think it will work fine if we move to a different menu when clicking on devices and then have the discoverable menu for creating new devices and the such. I might be wrong though and there might be no issues to how it is on a cellphone.
Anyway, love the game. Hope some of this was helpful.