100% realism is still far from 100% realism. In real life you don't push buttons to do something (well some buttons, but certainly not from a keyboard). You don't click a guy and make an order and expect it to be done, being a leader is much harder in real life, like erich topp said, you have to be familiar with everyone and everything and you need authorithy to be a submarine captain. Authorithy is not practiced with buttons, it is practiced with bravery, guts, testosterone, knowledge, insight and social skills. There are no time compression in a real submarine

nor is there a pause button for you to prepare TDC data. Simulation is all about fun but in a real ww2 uboat it was not fun, they ate bad food, feet was hurting, haven't got laid in weeks.
There are dosens of little things that is not so obvious, but in a real uboat you would see the obvious that it is completely different.
U-boat's is like driving a car and uboat simulation is like being a passenger in a car. What you see and experience as a passenger is a totally different experience than actually driving the car. Ever noticed you remember a route much better if you are driving the car yourself, but if you are a passenger you will not recall the route taken as good as if you were driving yourself. It has everything to do with first hand experience.
Even if simulation looks and feels the same, it is not the same, it just isn't. Every experience you have with SH5 can not be translated to a real uboat in any way, it's hard to understand but thats just how it is. Imagine yourself standing in a real uboat, your speak out to the crew members with your light voice and they don't even acknoledge you because of your light voice and lack of authorithy, a must-have for any uboat captain, if you can't even get through that barrier, everything else have failed.
It is easy to make the right decisions and think clearly in front of a screen, but in a real uboat, can you think as clearly under pressure and much noise and at the same time stay cool, keep your crew members close to you and make everything work both socially and technically
I am suspicious to the term "100% realism"
95% of the job is living in a 100 square metre "house" with 30 people around you, and the other 5% is gunfire. Make that 99% and 1%.