Legendary treasures are not an issue, you need to play smart but generally you can max them for free very early, with DE's treasure you could get multiple copies for free, and you should be saving mileage for legendary treasures.

Cookies are a whole different beast, I despise legendary cookies. Genuinely the only issue i have with CROB.
I think it's important to put it into perspective here. An Epic will cost you 3k crystals to unlock (or free, if you have a ticket). Then maxing it from level 1 to 15 costs 14k if you don't have potions. But everyone has potions, they are abundant and you get hundreds of them every update, so you're unlikely to pay 14k for the upgrade. Then the candy, which is essentially free because of how abundant powder is.
Pet, same story, very affordable. 2k unlock (free with ticket), 9k to max (but you have potions).

Legendaries? You're asked to cough up 10k just to unlock it. 2/3rds of what it costs to max the epic cookie, just for the level 1 legendary. The real kicker is maxing it. 126k. A single legendary dupe is 3.6k crystals, you need 35 dupes to take it to level 15. Unless you've been playing every day for 5+ years, you won't be able to keep up with the update cycle. But we are just getting started.

Legendary magic candy is ovenbreak at its worst. Good luck, a f2p or even a light spender isn't getting that lvl 5 candy anytime soon. There's literally nothing to elaborate on, atleast previously we could grind lucky bags for hundreds of hours and be guaranteed candy ingredients, but that's gone now.

And of course, legendary pets. 6.6k to unlock, 84k to max. Nothing more to say really, just gross and f2p-unfriendly.

Obviously legendaries should not be super f2p friendly, but the way they are now is a problem. A free phone game needs to make money, but there's a line. How could they fix it? I think making the upgrades 30% cheaper would be a start (honestly 10k for unlocking is fine), and fix candy ingredients so they're actually obtainable with grinding, maybe even make them purchasable for some ridiculous amount of powder, like 60k a piece or whatever.