I was surprised to see others commenting on other places I shared this agreeing with you that siphon is a problem, for me it was actually one of the cards that hooked me, just like the Breaking News/Scorched combo. I guess different people like this game for different reasons For me it was never a huge power card, especially back in the San San / Data and Destiny meta, when glacier was king, but it was one of those cards that could swing things your way if you saved it at the right time. Most of the time though, it's very easy to play around, and I'm starting to wonder if maybe the issue was that the original core didn't have the tools corps needed to play around it. I'm talking about things like cheap gearcheck ICE (oh, you thought I was gonna bankrupt myself rezzing this to stop you? Well, have a Vanilla!), defensive upgrades that either stop the run dead, like Caprice, or stop the run event from resolving, like Crisium, or high rez cost assets you could keep on the table to deny the runner those credits like Eve Campaign. Actually we did have some of that last on, there were expensive cards like San San and Adonis you could hold back for when the runner tried to siphon you, but with corp economy being so terrible in Core Prime, could you really afford to keep an Adonis in reserve for that?
Actually that last point might be the most important why a lot of people have soured towards siphon: corp economy was MUCH WORSE than runner economy in the original core! So Siphons were far more impactful than they are when playing with the full card pool. But it's possible that if you had a negative experience with siphon when first learning the game, your impression of it doesn't change, even if the card is nowhere near as oppressive anymore.
I think that with giraffe baby staying in Corp economy is much improved in Core 2.0, and siphon wouldn't have been as oppressive. Especially with the new cheap barriers they've introduced (Wraparound makes Crypsis sad!) and Corroder gone! Now the best use for siphon isn't to actually get money, but to force a rez, and with cheaper ice around, that doesn't slow the corp as much either!