Sharepoint - Single selection lookup column Vs Choice column of type dropdown

Besides your details descriptions in your question , The following points will let you know when you can use lookup field VS choice field ,

For a lookup field,

• You can manage permission at its list per list item to show and hide specific items at a lookup field based on user permission .

• Also, Look up field used when you need to make a relationship between two lists as one to many relationships.

• Use lookup field if you have many choice items .

For choice field

• You can use Allow 'Fill-in' choices: to let the users add values that not included in list

• You can show values as Radio Buttons and Checkboxes (allow multiple selections) beside the drop down list.

• You can build Column Validation and default value

If you detach permissions on the source list, end users (contributors) will not be able to edit it, but only select the item from the drop down if you set them as readers.

I would select the 'choice' feature when the list is fairly simple and the choices are not many (can be 3 to 50). One of the downsides of choice is that you must keep them in alphabetical order since the system will not sort them for you.

I would select the 'separate source list' option when the items are many (above 50).