You forget 2 factors here.
1) the oponent NEEDS Knock Off to stop this set.
Not really, Toxics work just fine since this piece of crap can't get rid of status conditions while Haze (Usually found on Vaporeon which, by the way, doesn't take crap's worth of damage from Ice Beam) effectively nullifies your "defense" of Double Team. Besides, just about any CB Sweeper out there could probably score an OHKO on this thing, CB Medicham in particular rips through it effortlessly.
2) It doesn't matter how often I hit the oponent 1 on 1, chances are they would run out of PP long before my PORYGON2 and will suffer unstoppable damage from STRUGGLE attacks.
Ever heard of switching? Your opponent could easily juggle between two ice-resistant pokémon (Say Snorlax and Milotic, both very common on OU teams) and avoid losing any PP at all while you play around with your little "strategy". If it can't trap it's not much of a drain on PP, especially with the PP up option being a forced rule on several servers these days.
This set was designed to wear down the oponents PP, not nesessarilly defeat them. The attack I chose was Ice Beam because it can hit any oponent. Weather it's effective or not is besides the point, the point is that it can hit all types and does not suffer penalties like inability to hit types like Dark, Ghost, ect...
On a side note, the oponent that can't counter this minuiver will be weakened for the next fight even if they manage to defeat my PORYGON2.
Lol, weakened indeed. Only losers are swamped by Double Team. In case you didn't know, hazers exist.
"The best offence is a good defence."
Double Team is a joke as far as defence is concerned and it's not like you get any benefit from more than six ones, anyway, so the Leppa Berry is doing you no favours whatsoever. Also, Sheddy is immune to Ice Beam and any given bulky water type can take em' without suffering any significant damage. -.- If you want to use Recycle you'd be far better of with
Porygon 2 @ Salac Berry/Petaya Berry/Lum Berry
Nature: Modest
Thunderbolt
Ice Beam
Recycle
Recover
Lum Berry + Recycle would provide status recovery while Petaya or Salac could improve its sweeping ability and Recover and suitably high defensive EVs provide durability.
However, its defensive abilities would be severely handicaped by the lack of lefties recovery and Thunder Wave (Which does provide the occasional parahax).
I could go on more, but considering your arguments thus far, I can see that logic doesn't apply for you so I won't bother. To the intelligent people around here, though, turning Porygon 2 into a lame and defective annoyer is a horrible waste.