It's not.
HB one is ONE extra champion + very little in game currency.
The Champions Pack is all ELEVEN current champions + FOUR more at-least through 2018 + any in the future + custom games access + three reliquaries loot boxes (the best ones which can only be bought with real money (through platinum) giving three drops each of with a better chance of good drops) + a buythroughearlyaccessgetthisRangerskinskin.

The HB one is more like getting access now as through the beta or future free to play and one champion. One champion do cost $4.99 but on the other hand the Champions pack cost $29.99 and give you fifteen + three cases which I think would cost $10 + one skin and they charge like $10 for skins too so .. Champions pack value would be more like $95 if bought individually.

HB pack like $6 from champ + in game currency + whatever you value access now to. Anyone could had gotten it before by signing up to closed or open beta. But not on Steam. Steam will happen when released and available as free to play. And then just with Ranger. You can hire champs for in game currency (given through playing and achieving daily tasks) and rarely get them in loot chests too though.

People who own the Champions can instead of hiring by the most basic backpack loot boxes with their favor and when they get a Champion duplicate / one they already have they will get a small amount of rubies instead, but it take like 15 such drops to get a skin set so .. It's a convenience factor and support thing to buy the Champions pack I guess and support & ego thing to buy anything beyond that.