For sure would be an upgrade. I don't think you have to be timid about it... Poeltl is simply not a vertical spacer. He's not a lob threat in the slightest - to the point where, during the bubble, I was kind of wondering if there's something with his knees that he'd rather avoid jumping to worsen. He's not a strong finisher either, neither as a roll man off a PnR or on the rare occasions he gets the ball in the post. No post game, no fakes, no hook shot, no midrange catch-and-shoot nor pullup, obviously no 3 - his "offensive arsenal" is literally nothing more than a soft floater on occasion, and the easy spoon-fed-by-PG points that literally any bench or starting C in the league could get. At no point has Jakob looked like a sure starter or came close to being a player who can "hold down the C position" for any number of years, tbh.
A team just can't be getting 0 offensive production from one of their players in this modern age, no matter the position. I'm itching for the Spurs to draft a big man, either a 4 but preferrably a 5, just so they don't delude themselves into giving Jakob a deal akin in proportion to what they gave DJ. That was a stupid move, and putting a lot of money on Jakob would be stupid as well. The sooner the FO realizes Jakob is a glorified bench C, the better, tbh. I don't care whether it's Okongwu, or Okoro, or Smith or Precious or even Wiseman by trading up. Jakob is not a starter on a championship caliber team - maybe not even a starter on a high seeded playoff team, unless he's very well surrounded, imo.