I know you can switch on lots of stuff under assistive touch but why can't the iPhone be like the iPad and have full on multi touch gestures available? is it to do with the tech/screen or have Apple chosen not to implement it?
Apple chosen to not implement it. With jailbreak you can use tweak called Tage which gives you many swipe gestures like switch between last apps, open app switcher, lock phone by swiping status bar.
Apple is slowly going to be implementing it. With the rumored all glass front panel with no home button will defiantly open the doors to any and all multi-Touch gestures. With the iPhone 7, we have multitouch to switch between apps, hard press keyboard to enable a "trackpad" interface. Once perfected we will see iPad "slide over" and possible PIP in the future.
Apple chosen to not implement it. With jailbreak you can use tweak called Tage which gives you many swipe gestures like switch between last apps, open app switcher, lock phone by swiping status bar.