Is it Pugna or Pubna?

I still think that the change to Life Drain to heal both HP and mana (!!) of allies is almost overpowered. Seriously, as long as you have mana, you can heal an ally completely and then drain the HP you lost off creeps. Infinite heal!
Actually I think Mekansm is outdated on him, IMO Bloodstone rush is way way better the way he works now. He absolutely needs the 500 HP and having infinite mana allows him to spam healing ults AND Nether Blast to his heart's content...it's a pushing lineup after all, the push must never stop. Besides Soul Ring is already awesome on him, you start with tranquils + soul ring.
I mean being able to push with your *whole team* being *permanently full HP and mana* is almost OP, it's really free Healing Ward with no cooldown.

Actually I have yet to see successful pub Pugnas. I remember that Singsing plays actually a pretty good sucky sucky, just rushing blink-Aghs and once he has the "positional sucker" he becomes a ganking machine.

Don't dismiss him too easily I think he's just in the "try out in next inhouse" list.

^^ see above a pugna working in pub game !

Don't you pick Io for that purposes?

Well you'll have big problems farming your heart and/or bloodstone on Wisp :)
However on a Pugna mid you can have your bloodstone really fast and then go push with it.

Pugna mid does nothing comapred to popular mids nowadays( Lina, Storm Spirit, Templar Assassin etc.), that's the problem. He just heals his carry, saves allies from evil Troll Warlord or Juggernaut occasionally, and that's mostly it, his ward is pretty situational.

Simply put, even as mid Pugan does what supports should do, and brings no damage or disables to the table aside from items he can get. Ans as a support he's pretty useless in lane and in ganks alike.

You cant compare him at all with those heroes, pugna is purely an extremely early hardcore pusher, and he does that better then anybody else.
Its just that pushing is really weak now, if a patch comes now where towers give more gold to the team he would suddenly be OP, since he has been buffed in multiple ways since the last time he was viable.