AbdulAlhazred
Legend
Not sure I entirely see it that way, in story driven learning still amounts to weighing the cost of acquiring the one or the other only so much time to be had you know, most cases we generally assume off screen learning for the majority of rpgs...
But I do like the context for onscreen learning like GMTs and similar, but requiring it all to be that way might feel heavy handed in a way, not sure, cut down to 20 levels like you do and other things interact with it.
That lesser boons not being artificially limited, with plenty of non-combat being lesser boons to encourage them might indeed be the element that gets the job done.
In effect HoML has nothing but 'GMT' in 4e parlance. I mean there are also items, but the form factor doesn't matter that much. The table can always decide of course just to what extent they want players deciding exactly which major boons to get, but the GM is always enabled to use narrative to set the possible world of choices, or to sometimes just give one out (and since each major boon triggers a level increase that means they have a strong control of that process if they want it).
I'm not 100% sure how the divide between major and minor will work out in a full game. I certainly think you're right, that a lot of the things that can be more easily narratively limited and don't add instantly to the power level of the character in a material way can be minor boons and thus taken out of the resource equation, though a GM might shade things by say decreeing that the acquisition of several related minor boons IS a 'major boon', that would deal with any propensity to 'sand bag' (though frankly I think of that more as choosing your style of game, so I don't think its an actual problem).
Anyway, no one approach is likely to work perfectly at all tables. My groups have always been pretty accommodating in terms of working out how things go and creating a fairly consensus-driven game. It might not work out so well at a table where the players are really militant about controlling all the build choices, which some 4e players are at times (so I hear, never actually experienced it in practice).
