The closer to accurate scale the more realistic detail you can bring forth.Even realistic games are often not really realistic at all
There are so many factory you need to consider, like visibility (too small), perspective (camera FOV of ~90 vs human FOV of almost 180 degree), thirdperson view (the angle of the camera let details/chacters appear smaller/larger), performance (render a football stadion with 20.000 seats or just 2.000 ). Best to take a 'realistic' game which would came close to your imagined game and analyse it. Walk through the level, take a really close look at the details. Compare it to the character.
Most often a single game do one thing really good (GTA: sense of large,living city) and this little thing is the reason, that they use a specialized game engine. And you will have a really hard time to copy this feature with an other engine. Engine are often tailored around two or three main features and seldomly are omni-potent.. Therefor, choose your engine by analysing comparable games. Watch trailers, ingame video, play demos etc. to help you decide, which game engine would be more suitable to your vision.
So what you are saying.... Is We need to make our own game engine???? hahaha Challenge accepted