Why can't developers find the perfect combination between graphic, FPS and loading screens?

Wouldn't surprise me if it was a combination between size of games and HDD limitations.

When you write to a HDD that 10GB game is spread across the disk and the fuller the disk the longer it takes to search especially as you erase old and write new content to it.  That's why defragmintation always made a computer faster it would place parts of a singe program/file next to each other on a HDD.

Because of SSD's taking over the performance segments (even £300 laptops come with 128GB SSD's now) HDD's are focusing on capacity at the expence of performance which is fine for external HDD's but not so good for consumer electronics like game consoles.

The more impressive the game, the more power it uses up.. and despite consoles being powerful, they last for at least 3-4 years, meaning that the system's tech is from that time..

Yeah it's a pretty annoying issue. Especially smaller details, such as in WWE 2K15 to create a wrester. You preview each article of clothing, or whatever, and the loading screen in obnoxiously long just to preview it.

Yes please!

I haven't had any huge problems with loading screens. For example, Ori only loaded in the beginning of the game, while Halo 5 loads reality quick. Is there a difference with physical games perhaps?

This is horrible... but at least Sony games are feeling next gen when it comes to loading screens. All games from them that I've played had small loadings. Hopefully third parties take their time to optimize their games better...

Despite having two SSDs (fantastic btw) my 7200 RPM drive still does well really well, even on large games (Fallout 4, MGS4). Granted that's on PC, none of my PS4 games take too long to load. Same with my Wii U (except AC3). I will admit that some games have ridiculous day one patches.

I think Nintendo does better

Sounds to me like you're playing the wrong games.