The “Collect All” button is useful for 1* / 2* / 3* heroes. The Devs make little money of them.
And 4* / 5* if you have the complete set of Classic 4* / Classic 5* heroes. The Devs are unlikely to change Legendary training.
But.
I still do not have green 5* Lianna. So the Devs want me to get excited, then be disappointed, every time I collect Legendary training.
Gacha freemium games are based on the casino model, so the Devs want the original button to be very similar to summons which has been carefully adjusted over years to maximize income.
I was happy, but very surprised, when the “Collect All” button was added. Especially with the leaked Hero Academy, I expected the Devs to resist the idea.
Notes
loot box mechanics
30x summons
Technically you can skip the summons animation by repeatedly tapping the screen during a 10x or 30x summons, but you still have to tap once per hero.