I completely respect your opinion on the ability to play Gandalf as a cleric or druid or whatever. But this is a great example of how your experiences and past seem to be trapped and isolated in a bubble.
You said "As was well discussed in the magazines of the time, you also didn't play a magic-user to play a Gandalf-like character. Gandalf was more often modelled as a cleric" and now you are referencing a single item from White Dwarf. I wouldn't be surprised that with enough digging you could find a stray bit of support somewhere in Dragon. But the presence of "Gandalf as wizard" was ubiquitous.
The problem here is a culture clash. The D&D wizard sucks at replicating Gandalf. According to a particularly notorious (and well argued) article in Dragon Issue #5,
Gandalf was a fifth level magic user. Gandalf was also the only member of the party able to go sword-to-whip with the Balrog, meaning that Aragorn and Boromir were both weaker in combat than a level five multiclass character.
For some groups "I wear a hat and can cast spells" is enough to say "I'm Gandalf". And for some groups the SCA version of history is more than sufficient to say they are reproducing history.
For other groups, "This character might be able to dress like Gandalf but behaves nothing like him and the game mechanics actively make it almost impossible to behave like him in almost any way" is a killer argument.
And there was a culture clash between the groups willing to put up with a D&D wizard in cosplay as Gandalf and those who actually wanted to play Gandalf when they were trying to play Gandalf. [MENTION=42582]pemerton[/MENTION] IIRC favoured Runequest at the time - which is less cosplayish than pre-4e D&D (actually the 3.5 Bard makes a pretty good Gandalf or Merlin, and the 2e one a just about passable one). The groups were self-separating (as many are).
I didn't get really heavily playing until the 80s myself. But the wizard = Gandalf or Merlin expectation was assumed to be true early on. Yes, people would play away from that type quite by design, all the time. But the foundation was well understood.
And from everything I've read right from the beginning the newbie expectation that the wizard = Gandalf or Merlin was well known. As was the sheer disappointment on behalf of many people when they found out that this simply didn't work mechanically. Until 4e the D&D wizard was first and foremost a gamist construct that in practice resembled nothing other than a D&D wizard (even "Vancian Magic" doesn't help the wizards behave at all like the wizards of Jack Vance).
Your comments on the differences between the mechanics and narrative are accepted without dispute from me. But the implication that Gandalf *could* have charmed someone was never a stretch. No one ever felt that an elf or archer could ONLY do those things that Legolas did and no one felt that a wizard could only do the things that Gandalf did. (Halfings tended to be vastly better thieves in D&D than Biblo, and Frodo was not really a thief at all). So the players "as Gandalf" would do the cool thing that they wanted Gandalf to do. And they would not get hung up on "Hey, Gandalf never actually did that." Pretty soon Fireball is the go-to spell. The perception over just a few months of play evolves from Gandalf could have done this to my Gandalf inspired magic-user does this all the time. The disconnect is there, and yet the understanding and satisfaction with that understanding and enjoyment of the game and *being Gandalf* was commonplace.
And here you are the one with a bubble. There were two separate groups of players - on the one hand were those happy to play an unashamedly gamist game and just wanted the excuse to dress their characters up as Gandalf. Those behaved as you describe. On the other hand there were the players who actually wanted to play as Gandalf rather than as Stock D&D Wizard #14 dressed as Gandalf. Those have all the problems [MENTION=42582]pemerton[/MENTION] outlines and left D&D for other games that actually allowed them to get within hailing distance of the characters they wanted to play because Gandalf spamming fireballs is not Gandalf. It's not "Do not meddle in the affairs of wizards for that suit of armour makes a good roasting pan."
There's nothing wrong with wanting to play someone inspired by Gandalf and that wears Gandalf-like robes. And there's nothing wrong with wanting to play Gandalf. But pre-3e D&D only caters to the former group (unless you delve deep into 2e and specialist priests).
