Isn't it pure cosmetic loot boxes? Who cares?
As Nintendo said, loot boxes concept is nothing new, just look at cards. Pokémon cards, baseball cards, magic gathering cards, ect. You never know what your gonna get buying them.
Hell, I'd be more upset in regards to the online card games like Pokémon, the WoW card game, elders Scrolls cardgame, ect. Those, you can be complete shit without good cards which you need to for the most part spend money to get at a reasonable at all rate. I would ban those things as gambling way before a cosmetic vehicle skin.
These are fundamentally different as there is no trade system in Rocket League.
Pokémon is literally a trading card game - the whole system is based around getting random cards and being able to trade them with your friends for ones you like better.
The crater system in Rocket League replaced normal DLC were you just bought a car and cosmetics you wanted. Now you pay and hope to get what you want - only way to try to get it again is to pay again. That's more nefarious than Pokémon or Magic in my eyes.
Again, pure cosmetics versus actual gameplay items.
I would say gameplay items/cards is more nefarious. Think of Pokémon again. I could get a Charizard card easy enough. Little more luck involved to get a reverse holo of the same card. Super insane luck to get a holocard, or possibly even the full art version. Again the card plays EXACTLY the same in all scenerios. Same stats, just looks different. If they made the base Charizard card a 1 in a million chance, then it's BS, but if they make that super easy to get and the others each incrementally harder to get then its fine. For gameplay reasons, you are not gimped at all.
And then again to card games online, such as WoW's card game. Strange I can never remember its name. Can you trade in that? I don' think so. You can't trade in Yu-go-oh's card game online. So again to get a better deck to not suck you need to rely on loot crates. Rocket leage on the other hand, you are not gimped at all whether you have 10,000 hours on your save and 1,000's of dollars spend or you just installed the game seconds ago and not spent a dime on it. You could still go in and kick that person ass who spent thousands of dollars on cosmetics. You can't do the same in card games.
(I havne' tplayed rocket league, so there may be some rpg elements that raise your cars effectiveness for all I know. I'm under impression game is just purely same identical cars under the hood that all just look different.)
Or take a game like League of Legends. That game has many unlockable characters, but they are all supposed to be balanced, so whether or not you have someone unlocked or not should not make you uncompetitive. But again card games like Wow, pokemon, yugioh, ect you need good cards to even stand a chance. No starter deck will last a second against a good deck even if that person has the worst draw luck in the universe.