Meh, the conversion thing is a matter of both expectations and of needs. When I converted my setting over from 2e to 4e I naturally had to eventually translate the stats for various NPCs and retired PCs where they existed before. I didn't find that at all difficult. I also wasn't THAT concerned that some very specific spell or power had to exist in a certain way in 4e. If it was some sort of 'story ability' -something that explains the NPC's role in the setting- then it just got made into a ritual or simply decreed into existence for that character (they are NPCs after all, 4e is big on free-form NPCs).
IF I were to proceed with conversions of PCs, and the only ones I ever did were a few of my own high-level 2e ones just for amusement, then I didn't find it that stunningly difficult. My Ranger that got assaulted by Demogorgon cultists and started a crusade against them (he eventually basically went insane he became so fanatical) is perfect as an Avenger MC into Warlord for instance (to get some STR-based bow stuff and a few leader powers). I might do it as a hybrid if I did it again. That came out great, as the character was a level 12 2e ranger IIRC that was mostly using a single greatsword and sometimes a longbow. Most of what made the character what it was was the personality and story. Obviously you want to be able to use your signature weapons, but that's not really super hard. I really couldn't care less if I had exactly powers that mirrored whatever the heck spells he once had, those were not really a key part of the character and didn't even get used THAT much. I could always pick up an item or maybe a boon to emulate one if it happened to be really significant.
Likewise other high level PCs I remember tinkering with. My wizard was pretty trivial. He's not quite the combat monster he was at level 14 in the old days, perhaps, but rituals and a judicious choice of items and implement gave me a pretty solid "seeker after all the world's hidden knowledge" type adventurer. AD&D Assassins are pretty simple as a Brutal Scoundrel rogue build, maybe with a shield proficiency thrown in if you want.
I know some people will just dismiss it as "that's just your opinion", but I feel like the people that had to do all sorts of intricate 3-way MCing and picking 12 different options from supplements in 2e were more enamored of specific rules minutia than they were into RPing. Its not that I never made a character that was a MU/FM/THIEF or some such thing back in the day, its just that the exact verbatim letter of what that character could do in a specific situation wasn't the point. In 4e I might well leave out the FM in that character as not really adding something distinct that needed to exist in the 4e version (IE as a rogue he can already wield weapons and wear armor appropriate to that sort of PC). I might even just look at it and make the character a Bladesinger and take some training in Thievery etc. or something like that. I have now a sneaky blade-wielding caster. I can always take an MC into rogue, pick up ritual casting, etc as desired to fill in a few niches.
One of the major reasons I DO see 4e as a perfectly legitimate successor to previous editions of D&D is the very way that it consistently enables the same sorts of character concepts and archetypes within the same sort of milieu. I never found that other fantasy games I've tried back in the day did that nearly so well. GURPS Fantasy, Swordbringer/Elric/RQ/BRP in general, RM, etc never quite hit the same note. Characters had very different power curves, magic filled a very different role in the game, or other things. 4e OTOH focuses on mostly the same things that previous editions did. Even if spells are now 'powers', they are still filling very much the same role they did in the old days, and the limitations and benefits of casting are not radically different. Now, TODAY there are modern game offerings, mostly d20 variants, that come much closer, FC, SW, 13A, RRPG, etc. You can do a pretty decent 'D&D' with them, but there are still some differences. 4e is still closer IMHO to previous editions of D&D than even any of these other newer games, often even when they are at least as mechanically close to 3e D&D as 4e is.
Also, I'd have to say that FOR US 2e -> 3e was at least as major a shift as 2e -> 4e has been. We never used all the kits and blah blah blah from 2e really. We just found a lot of that stuff mechanically poor and ill-considered and mostly stuck with core 2e. Now and then we'd use a few carefully chosen options, but our characters were always pretty tame in terms of rules usage. 3e to us was a huge leap that we never really cared for (mostly) with all its focus on tons of character options right in the core. 4e certainly was a leap as well, but not MORE than 3e given how we played.