This is purely a matter of opinion and mine differs to yours here. Yes, the CM three put in a major shift which is really noticeable like Henderson doubling up to help Trent against Zaha on numerous occasions on Saturday. But as you say, its nowhere as simple to suggest we would immediately lose anything that we currently have by not having Henderson, Gini or Milner in the team. It is highly, highly possible to have the best of both here. Gini and Henderson do get up the pitch and perform adequately in general, stellar on occasion and abysmal on occasion. There is no reason to believe that our entire style would change by getting the likes of Havertz, who is imho De Bruyne light at this stage in career.
If you think that what we have is the be all and end all and that no improvement can be made and that this should be our midfield go to for the foreseeable future then that's great and we will probably continue performing to an brilliantly high level which is awesome but I believe we have the chance of a once in generation team that could go down as one of the all time greats by acting while we have the stellar talent in the team already.