in over 2 levels I dont have enough blue essence for a 4800 champ.
I don't know the formula exactly, but I do know that, in terms of Champion Capsules (the rewards from levelling up), any given Champion Shard you gain will have a randomized BE value (Champions in 1350~ range, 3150~, 4800~, etc.), but their disenchanting value is actually substantially lower than their listed value.
However, Riot has noted that the Champion Capsule BE values are a little dissatisfying and unrewarding, and have been working to rectify it, with their first and foremost change being giving Blue Essence straight from First Win of the Day bonus. I imagine that they're looking to further explore ways to make the BE gain more satisfying, but otherwise, I don't have much in the way of information on that front.
In over 10 chests Ive gotten only enough orange essence for one alistar skin and rerolled the rest for a galio skin.
I imagine this is referring to Hextech Chests (rewards from Champion Mastery), which, Orange Essence is a currency reserved for cosmetics (Champion Skins, Ward Skins, etc.) and are separate from BE. However, Hextech Chests also have a random chance to drop Champion Shards and Blue Essence (I recently got a Shaco Shard and 150BE from one), but their drop pool is so vast that I wouldn't count on Hextech Chests as a reliable source of BE.
My question is why is it not rewarding to play the game and why do i have to use real currency to get new champions at an effective rate.
As mentioned above, it's sort of an accidental design reservation on delivering the BE change - something that was kind of to be expected with the massive update that was Preseason 2018. Also as mentioned above, Riot has stated that they're working to make the Blue Essence gain from levelling more satisfying. Hopefully it happens relatively soon after the new Season begins, but elsewise, I hope you find your next few level's worth of BE to be bountiful.