I'd actually say that the opposite is more true.
+1 magic weapons can put you above the curve, and that can be fun, but the best magic items give you new abilities. Also, DMs tend to balance out magical item attainment. It won't be all at once, but generally you eventually find something of an equivalent to that +1 sword for other party members.
I'd also say there is a mental element hear that you nailed. To botch a quote from Captain America "Who are you without the suit?" If the fighter has a +1 weapon I know it isn't because they are a better fighter, but because they have better gear. If I had the same gear, we'd be evenly matched. This is also why I don't like the "solution" that I've seen before that if a player is behind the curve in terms of ASIs that they just get given better items. It feels like a crutch.
Now, one place that I can sort of see this being a bit more murky, are items that increase spell save DCs. Not only are these items incredibly powerful, but they are far more powerful than a simple +1 to spell attacks. Because they allow your daily abilities to land more frequently, and raising that is something you can't do very often, and may even be impossible to do depending on your scores.