I think I'm going to accept that I can't explain it that well and bow out of this.
It certainly wasn't my intention to try and bully you into bowing out, and I hope I haven't done so.
I'll have another go at restating the view that underpins my posts in this thread.
Upthread, another poster said that, before roles, for many players (perhaps most) what drove their character building was a conception of the character as "a warrior", "a shaman", etc - some sort of fantasy figure or archetype.
My response was that if a player describes or conceives of his/her PC as a miracle-working healer, but mechanically the character in question has no ability to work miracles, heal injuries, etc, then something has gone wrong. In other words, I think it is fairly key to a roleplaying game that mechanics and fiction complement one another.
The role labels in 4e are pointers to mechanics, with an eye to linking those mechanics to fiction.
This also relates to my exchange with [MENTION=92511]steeldragons[/MENTION] upthread. I stand by my comment that to describe the role of a warrior as (say) solving the problems the game poses by strength of arms does not give the right sort of information to help players build characters where the mechanics and fiction match. This is because it simply a statement about the fiction - the warrior solves problems by strength of arms - but it tells us nothing about mechanics.
A swashbuckling Errol Flynn type solves problems through strength of arms. So does a knightly Lancelot type. So does a Jet Li-style martial artist. But in most fantasy RPGs they are mechanically rather different, and not necessarily all equally viable. (Robin Laws' Hero Wars/Quest might be an exception, and maybe other free-descriptor systems like FATE.)
To give some examples of elements of action economy and broader action resolution that matter to this sort of thing, in Rolemaster being surrounded by enemies in melee is extremely punishing, because most defence comes from parrying, and parrying is limited to one target per round. In AD&D, being surrounded is less punishing because most defence comes from AC, which is pretty constant across all targets (there are a few issues about shields and flank/back attacks). In Marvel Heroic RP being surrounded is not especially punishing at all, because defence comes from a reaction roll and there is no limit on the number of reaction rolls per round.
To try and make Jet Li-style martial artists viable in RM, there are special rules whereby unarmoured warriors can obtain a parry-like defence that applies against multiple targets. To make Jet Li-style martial artists viable in AD&D, there is the monk class (which gets a level bonus to AC) and the rules for kensai and martial arts in Oriental Adventures, which also allow the gaining of AC - ie all-purpose, multi-target defence - without having to wear armour.
I would expect a player wanting to build a Jet-Li style martial artist in either of those systems to have regard to those rules, which establish the mechanical framework within which s/he is able to realise his/her character concept.
Turning to 4e: if a character wants to play a swashbuckler-type, who is mobile, hits hard, but is vulnerable to being surrounded and taken down by mobs, s/he should start by looking at the classes labelled "striker". If a character wants to play an uber-dreadnought type, who is happiest when surround by enemies that s/he is beating to a pulp, then s/he should start by looking at the classes labelled "defender". (This also alludes back to the "strong guy" discussion upthread - this is why [MENTION=22779]Hussar[/MENTION] thinks that characters like Superman, The Hulk and The Thing instantiate the defender role - because they do their thing most effectively when surrounded by enemies that they are beating to a pulp.)
The function of the role labels isn't to tell anyone what to do, or how to play a character. The rules - for PC building, for action resolution - nowhere reference the roles. They reference class, ability scores, sometimes power source (arcane, divine, martial, etc). The role labels aren't prescriptive - they are information-carrying labels that, in a rough-and-ready way, indicate what sort of fiction the mechanics of a given character class will tend to produce, if played in the default way.
The roles are somewhat prescriptive for
game designers, in the sense that game designers are expected to build character classes which can function effectively in one (or more) of the roles the game acknowledges. The prescription is, in my view, not all that tight - if you look at the way the game evolved over time, you see a wider and wider variety of classes and mechanical options within them (sub-classes) being published.
[MENTION=6680772]Iosue[/MENTION], upthread, said that the level of system mastery needed to build a wide variety of PCs in 4e is greater than in 5e. I've got not reason to doubt that - as a long-time Rolemaster player whose current group has its origins over 20 years ago with hardcore university wargamers, I've got a high level of tolerance for system complexity and so am not badly sensitive to its presence. I know that my players will spend their own spare time reviewing options for their PCs looking for choices of feat, power, etc that either singularly or in combination will produce the build outcome they want. I can see that people who don't like working with a complex build system would find it harder to build a range of characters in 4e.
But even then, for me the main complaint would be that the game only permits the building of a fairly narrow range of characters; whereas 5e might permit a broader range of characters. It wouldn't follow that those 5e characters don't have things that they are better at or worse at, as a result of the mechanical abilities that they possess. Bounded accuracy can mitigate some of that, in the sense that even someone with a less-than-optimised bonus can still have a go; and Iosue has given an example upthread of how that opens up some build options that aren't easy to achieve in 4e. But 5e PCs will still have things that they are better at and things that they are worse at, as a result of the abilities they have, which are the result of choices made by players in building them.