Respectfully,

https://en.wikipedia.org/wiki/Probability

I think you should change the concept of getting legs and mythic heroes, state that after a certain number of shards you have to get one leg or a mythic champion, this is especially true for void shards, whoever gets a leg on a void shard is a very lucky person. I really think that should be changed. It's all getting a bit frustrating.

plarium does state that after a certain number of shards, you will get a guaranteed legendary or mythical champion.

unfortunately, that number is 220 for ancient and void shards, 59 for sacred (except during a x2 event which drops it to 56), 174 for a legendary champion from a primal, and 210 for a mythic.

I don't know whether to laugh or cry. I'm torn between these two feelings.

Yeah here is the screen with the "mercy" 

i

Base rates

i

If you hadn't looked at the screen by clicking the i on the summoning page. So yeah as Carpe said basically you have to pray to RNGesus.  I have only pulled 1 Mythical from Primals so far lol. 

Oh and Remnant summons have their own mercy as well 

i

After 2400 of the essence and not getting a mythical it goes up by 1% per. So if you fail 24 times, you just have another 98 more tries if that 97th one at 99.5% fails as well lol. Total of 122 pulls. If you do all of Grim Forest Hard and Cursed City Hard a month you get 4 chances a month. So 30 months to hit mercy cap guarantee if unlucky. Almost 3 years. If you can only get 100 from Cursed City and 200 from Grim forest it is closer to 40 months lol.

I always feel like the 2x is a scam, I never see any difference with normal rates vs 2x, think they just say it's boosted and hope people believe them.

a 12% chance of pulling a lego is an 88% chance of not pulling one

2x Sacred my least favorite event in the game.  Seems to always feel bad for me.