Ultimately, the "problem" with magic items is not whether or not a character has them (or how many of them). It is whether or not characters are intended to migrate among different campaigns, because every DM has their taste about how much or little magic exists in their world, and thus migrating a character from one campaign to another may result in the character's items being over- or under-powered with regard to the rest of the party. It's not a matter of being balanced in your own campaign because the DM knows what items he is giving out and can ratchet up the level of opposition - it's a matter of being balanced against other campaigns... in other words, it's about homogenizing the D&D experience.
This is just my feelings, I have no data to support this other than playing D&D since about 1983. My sense is that there was quite a bit of cross-campaign-jumping very early in D&D history, to the point where it made Gygax grumpy to have to adjudicate among DM's as to what the "right" power level was, though it seems he personally seemed okay with any power level that a DM wanted within a campaign, he knew it was problematic to cross campaigns (I remember a sentiment - maybe in Dragon Magazine? - that Gygax and Co. were annoyed by fans that approached them at conventions to tell them how they had slain Thor and now carried Mjolnir and had the most powerful character ever and of course the derogatory term "Monty Haul campaigns" was around by the end of the 80's to reference campaigns with a high level of magic items). However, it's important to remember that the default assumption early in D&D was that all local campaigns were set on the same world (remember, in the really old school stuff, each DM was running a DUNGEON, not a full WORLD) and that there would be hopping around from group to group. For the most part, once you finished Alice's dungeon, you needed to go to Bob to run his dungeon because Alice was out of stuff for a while. Since there weren't thousands of pages of published supplements yet, everything had to be homebrew originally - lots of prep work for a DM!
By the time 2E rolled around, I think the norm had shifted to most players remaining more or less with the same group of friends - campaign-hopping wasn't really a thing as much, though there were still horror stories. DMs had graduated from managing their "one dungeon" and were now world-builders, and everyone's world was a little different - even if you were using a "published campaign setting." There wasn't a need to cross over to another group when you finished a dungeon, because your DM had more dungeons - and wilderness - and other intrigue - ready. The volume of published material that had been produced by this time really helped - you had tons of pre-fab adventures at your fingertips, from full adventure modules to 1- or 2-page entries in a Book of Lairs - so prep time could be drastically decreased.
3E built "expected magic items" into the system - probably at a higher level than most campaigns were used to - but it allowed a way to regulate campaign-hopping because you could look at the value of a character's magic items to see whether or not the character would be over/under-powered relative to characters of the same level in other campaigns. 4E pushed back hard on magic items, moving more to class abilities so that it wasn't really possible to be over/under-powered. 5E landed somewhere in the middle, but I think is still on the side of relying on "class abilities" for characters to do cool stuff and nerfing of magic items to allow cross-campaign homogeneity.
Players, of course, like cool magic items that do stuff. Some DMs like them, some tolerate them, and some hate them. The problem is not the magic items themselves, it's trying to homogenize D&D to appeal to all the tastes - you just can't do it. If players weren't inclined to compare their characters against others' characters this would be less of a big deal, but we're human, and we all want to show off a little bit... so I don't think it's possible to settle this debate to everyone's satisfaction.
It's like driving - everyone who drives faster than me is a maniac, everyone who drives slower than me is an idiot, and then there's me, the perfect driver. Everyone whose campaign features more magic items than mine is a maniac, everyone whose campaign features less magic items than mine is an idiot, and my campaign is perfect. Whether or not magic is "too much" or "too little" varies by taste and can really only be done by comparing across campaigns - which we shouldn't be doing in the first place since every campaign is unique. The only time homogenization is "needed" is in large shared settings ("Living Greyhawk" or the like) where there is an expectation that all the DMs will be running the same adventures in the same game world, and that largely isn't the case for most home campaigns any more.
I think some gamers today take for granted the number of supplements (both "official" TSR/WotC and 3rd Party) that have come into being since the early days of the hobby and for the most part it all builds on each other. Even if the rules are slightly different across editions, maps, plots, ideas, and characters are easily ported and converting monsters for combat is not that hard. DM prep has never been easier - not only is there a boatload of material out there to steal from, there is a collective knowledge of "how to do things" and "what to expect" that didn't exist decades ago.