Ohh, I get it. From reading his responses, the OP doesn't actually know what proxy farming is. Blue team Singed is farming Red minions at Red teams inhibitor turret. Blue team top lane champion can: Farm minions under his tower or walk back to his inhibitor and try to chase down Singed.
By farming by the inhibitor turret and pulling the minion wave into the jungle, Singed makes the enemy spend a solid 10+ seconds walking back to him... And since farming under tower takes time (9 tower shots? Two per melee, one per caster?) so you are going to be spending at least 10 seconds farming the individual wave if you want all the gold. So stepping back from your tower to try to get Singed guarantees at least one minion wave missed, two if you don't immediately run backwards the moment you reach him.
If the enemy farms under tower, his tower takes damage and he never interacts with Singed. If he tries to walk back to deal with Singed, Singed just walks into the jungle and the enemy loses the wave at tower, if he chases Singed in hopes of killing him (Which is hard, because Singed runs ghost) he loses 2+ waves.
A kill is worth ~300, then ~275, then ~220 if on the same target. Two minion waves early game is worth ~240 gold, ~280 if a cannon is missed and the value only goes upwards. So, even if Singed doesn't get away and dies at the cost of the enemy top lane losing two minion waves (Which they will if they chase you long enough to kill you), you go pretty close to "even" on gold value of dying. It is still bad, because you aren't farming while dead, but it get to be more and more valuable the more you die. Unless, of course, you just walk into the enemy inhibitor turret and Execute. When you execute, you lose almost nothing because your opponent is missing waves to get to you, so they miss both gold from minion, XP from minions. You end up getting (Way) ahead in gold and XP if you can execute.
At the same time, it is this brutally annoying thorn in the jungler's side. Because he KNOWS you have his top side jungle warded. If you are high on HP, you can miss a wave yourself to go counter jungle him. If you are low on HP, you can see him coming and execute before he has a chance to kill you, wasting his time.
So, often, you find yourself being left alone when you proxy, which gets you 100% perfect farm because... Well, you aren't competing with your own minion or tower ever for them, so you always get them. And, more quickly than you would think, the enemy top tower dies unless the laner is actively tanking the minions... Which only works if they have a ton of sustain/shield.
Which is why we saw Looper dominate a game at worlds with Proxy Singed. Yes, Singed is good enough to have been played at worlds and do very, very well.
And, on the topic of Garen, he does okayish. He counters a few things pretty well, and is countered by ranged champions pretty hard. He could use some buffs, but he is still fun to play.