We've sacrificed solo lane morde to get bot lane morde

From what I've seen of playing him so far and seeing others play him, it seems like he is indeed situationally effective in the bottom lane. If your support is the right kind of support who can make up for your low mobility and lack of CC then it's possible to make it work - e.g. Morde + Naut. Doesn't always work, but it can work.

And in exchange for this, we've lost top lane Morde and mid lane Morde.

The problems he's having right now in top/mid are as follows.

He has no access to his W for solo laning. This was used for everything from range farming/harass to a self buff to duke it out with an opponent - it was actually morde's strongest source of shield generation in extended melee trades

Siphon strike got nerfed hard but the hp costs remained the same.

Most of his power has been shifted into mace of spades which will practically never be used to it's full potential unless an opponent makes a mistake or an ally helps you out.

The time span for you to use mace of spades once activated is FAR TOO SMALL considering morde's incredibly slow attack speed and incredibliy slow move speed - why does nasus get to hold onto siphon strike for 10 whole seconds while morde has to use his ability within the 2 second window he's got?

His base mobility has been nerfed to Anivia/Nautilus levels which makes him easier to gank than ever since he doesn't have the CC they have. This makes solo laning harder than ever as morde was the easiest champ to gank in the game before and he just got easier to gank.

His base attack speed has been nerfed to the point that building attack speed on him is not cost efficient it, even a triforce won't crack him past 1.0 attacks per second. Yet mace of spades which is his strongest ability depends on attack speed to be cranked out quickly.

The problems with tring to fix these is that now since he's been forced into the bottom lane, any buffs to make him viable in solo lane again may make him monstrous in the bottom lane. It's not going to be easy to give morde the buffs he needs to be viable as a solo laner.

I'd say the things he needs to viable as a solo laner are Access to W in some capacity Massively increased base attack speed Move speed restored to 340 Reduced hp costs on siphon strike The window on his mace of spades should be atleast 5 seconds between strikes