This hasn't been an annoyance just recently, this has been long standing. 2 main use cases for me (in either the 'recents' or 'favourites') list:
1) when scrolling through either list you can easily accidentally dial someone by simply touching their name causing misdials (end up with someone calling you back asking if you called them, blah blah)
2) when ending a call (assuming you are already on one of the lists), the timing of pressing the end could easily cause you to touch the name on one of the lists causing misdials again
When Apple changed this to have the one touch icon moved to a specific circle on the right, this pretty much eradicated the above two scenarios for misdials for me whilst also keeping the convenience of one touch dialing, so for me it was the perfect compromise.
In terms of why its a big deal...from my own personal situation I use my phone for work, so yes, I receive and dial out pretty much constantly through the day. I regularly have a handful of misdials daily which doesn't sound like much, but spread over a number of years its a pesky annoyance that I would love to remove. I'm pretty sure even if you don't use the phone that much that there are users on the forum that would agree it would be nice to get rid of.