They wouldn't have to hold hands, but it's clearly doable to have a companion react intelligently to enemies.It still wouldn't have worked because often other characters are traveling with Joel & Ellie. People like you would just complain about how unnatural it looks for two grown men to be holding hands or walking on top of each other, character models clipping into each other, etc.
And I disagree with your other assessment too. People don't play it because of some sort of amazing gameplay mechanic. Mario is probably the most recognizable series in all of gaming because it was one of the original, most successful games of the 8-bit era. People play for the nostalgia factor, and ease of use/simplicity. When was the last time you personally played Super Mario Bros on NES?
And I just played back through Mario 3 a couple weeks ago.
And you wanna talk about a cliche, reused premise for a story? How old is the "man saves princess from monster" trope? Why aren't y'all bytching that Mario jacked it's premise from every fairy tale ever? But Mario's still a GOAT, huh? You two are fukking clowns.