Enma is more of training tool. Shisui is stated by Oda to be superior
1) Where? Can u give me the canon source? A sbs?
Or are u maybe referring to their grade? Ofc a black blade > white blade,
but if u haven't the ability to turn a blade to a black blade this doesn't mean nothing.
2) Every weapon is a "training tool" for a swordman.
Do u really think that mihawk didn't became more strong while he tried to control yoru?
Or are u really sayng that if oda decided to gave black yoru to mihawk when he was a teenager he would have turn into a top tier suddenly?
The training is the real power up here. And enma
have required an hard training.
Zoro managed to perfectly used shusui during the timeskip with mihawk. In wano, he wouldn't have obtained a new power up with the same sword.
The fact that shusui was and is an higer grade weapon doesn't mean nothing here.
So "wano if zoro kept shusui" is almost the same as "mihawk's life if he kept his first sword", the only logical answer is: he wouldn't have gotten that strong.
3) Zoro would have discover acoc like luffy? Maybe. But oda decided something different for him and enma was his power op.
So no, wano and ongashima would have been very different and zoro would have died against kaido or king if we rely on what we saw in the manga.
In a different timeline, oda would have decided for a different way for his power up and yes, nothing would have changed.