You see i'd say that street thug with a knife shouldn't be easy to beat, he knows his territory, he's desperate, he's tough from growing up hard and that knife he's holding only takes a few pounds of pressure to carve through flesh and make the protag dead as disco. Just because you're competent doesn't mean you're invulnerable in my eye. I actually think Torment got this about right at the beginning, the Hive Thugs were a fucking handful, okay for a combat Nameless it was far easier especially with using Morte, but still a good example to me.
I'd say it's just power levels gone off the chart, old AD&D used to be quite reasonable and most characters (except higher level spellslingers) weren't the superheroes we find in games now, you saw a Beholder and you fucking ran like a Nun seeing schlong. Problem is to me that devs have lost track of realism in their games, they think that just because you've got a hundred ton Dragon flying like an Eagle or a Wizard throwing lightning that there doesn't have to be any realism, internal consistency or rules. They've got it wrong at base, the Dragon and the Wizard are fantastic elements, governed by their own laws in game and with just as many restrictions and weaknesses as anythying else. Physics should still work normally, mortality should still be precious and folk should still act like folk do, but there's weird shit to react to and take into account, the fantastic.
Tolkien got this right in my opinion, yeah his world never moved on and other unrealistic shit but folk got hungry and thirsty, Hobbits took one wound and were fucked, men got downhearted during sieges, runners couldn't run forever and even greatest men weren't above corruption. Had a nice gritty feel to it, even though most folk cite it as the highest of fantasy. If he'd only told the Elves to fuck off...
As an old GM I never did any of the overpowered stuff though, one reason why I weren't a fan of Sword Coast and Realms were power level, strangely enough thought Dark Sun was much more reasonable there even though everbody began at third level.