Is this intended? - Shaco ZERO ap Backstab vs Critical

So I was chilling in the dragon pit, contemplating the landscape on the practice tool mode, then I decided to try some critical build because why not..

At this point I had ZERO ap, I spawned a Victime to victimise , hit him right in the face, then backstab the **** outta him.. I realised I did the same amount of damage backstab and forward.. Then I seems to have understand how it works.. Basically, if you have 0 AP and crit backtab, your crit (200%dmg) take over the Backstab passif (130% dmg) so its a simple crit, if you have ap it adds to your crit (200% dmg + 40% of your ap from your passif)

I might just be late to have understand it, but if you want to build full crit (100% chance) or even not full crit, without ap because come on you're not a mage assassin, you can't take advantage of your passif, how can you feel rewarded when backstabing your fellow ennemies?

TL;DR If no ap your backstab passif is useless when building 100%crit of even just when you crit cause it proc the passif but only apply 200%dmg (basically, a normal crit)

** ? IS THIS INTENDED RIOT ?**