No.
You have 97.5% chance to get a Rare or Epic hero.
You have 2.5% chance to get a Legendary hero.
You have 51.2% chance to get a single Legendary if you have received any.
So 1.28% in general.
You have 0.8% chance to get 3 extra Legendary heroes if you have received any.
So 0.02% in general.
It is said like this :
For each summoned Legendary Hero, you get 3 bonus draws, each with a 20% chance to get another Legendary Hero.
So if you catch 4x5* with a ten pulls you had to play lottery instead of this game 
I forgot to add insert extreme sarcasm
Didn’t read thoroughly till I saw your post. 3900 gems per 10x. 
Summon costs inflation is like hero power growth: tsunami strength and speed.
And when you get lucky and pull a 5* in your ten pull… It’s Reuben!