Since the hero collector rewards for hiring specified heroes are one time only you should allow the option to hire heroes through hero soulstones,hero shards,chests,hero cards etc. aswell so f2p players could progress through game aswell and get elite heroes.If the hero collector rewards were obtainable multiple times it would then make more sense to put the rewards obtainable only through hiring heroes with gems and honour badges.
While I don't see an issue with hiring the specific heroes with cards, shards or soulstones, as far as I know there are no hero chests to my knowledge, but the addition of these methods might aid the F2P community slightly as most generally won't have those spare resources available to hire the heroes.
Further the event is designed to give members a chance to grab some relatively free resources and not to stock up on them, so I doubt the suggestion to allow members to these rewards multiple times.
Just my 2 cents
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something tells me if this was an option we wouldn't see any elite or ordinary heroes in hero collector, as i think it is all about buying gems in order to roll those heroes. But it would be good way to do it.