The difference with Bender is that he doesn't show any of the fluidity in his game that Porzingis did last year. Porzingis was a capable regular on his Euroleague team while lacking the physical strength which we knew would come in a couple of years thus having huge upside. Bender already had a solid physical presence yet can't even get backup minutes on his team and is another guy who, like Hield, could easily be a pick that his team regrets.
I think this is unfair to Bender, and lacking a lot of important context. I'm not taking anything away from Porzingis - and I think he was the more impressive prospect going into last year, but here are a few key caveats.
#1 - Bender was born in November 1997. So at the time of this draft he is going to be 18 and 7 months. Porzingis was born August 2, 1995 and was almost a year and a half older at the time of last year's draft. The much more analogous comparison would be when Porzingis was slated to be in the 2014 draft before he withdrew (and there was talk that the Celtics had made him a promise at 17).
#2 - I'm mystified where you're getting that Bender "already had a solid physical presence" in contrast to Porzingis. He's listed at 7'1, 225 and is very thin. Scouting report after scouting report talks about his need to bulk up and add physical strength because he gets pushed off the block constantly. This is borne out by the clips available on youtube and elsewhere. Porzingis was listed at 7'2/7'3, 230 last year and was also very thin. If there's a difference in how filled out Porzingis was last year vs. Bender this year, it's not an appreciable difference.
#3 - As I already noted, Porzingis in 2014-15 was a full 16 months older than Bender, and he played about 21 minutes a game between the domestic Spanish league (a league with the excellent Barcelona and Real Madrid) and the Eurocup competition (second-tier competition - analogous to UEFA Cup in soccer). Porzingis had a very nice season, averaging 11 points and 4.6 rebounds and was named Rising Star in the Eurocup competition. But it's important to note that Sevilla was a very ordinary team without a particularly illustrious history that was perhaps more open to playing their younger players. They did not even make the 16-team knockout stage in the second-tier Eurocup competition and finished 19-31 overall on the season.
Bender, on the other hand, plays at Maccabi Tel Aviv, a team usually at the top of the Israeli domestic league (not as good as the Spanish league, but still better than many European leagues), and has an impressive history. Maccabi beat Real Madrid for the Euroleague Championship two years ago in 2014 under David Blatt. This year, Maccabi went 24-9 in the Domestic League, but had a disappointing year internationally - going 4-6 in the Euroleague and failing to advance from the group stage - leading to transfer to the Eurocup. Maccabi then went 2-4 in the Eurocup and failed to advance to the knockout round. Regardless, Bender played for a better team. He played very little in the international competitions and didn't get off the bench in last night's first domestic playoff. In the domestic league schedule, he played more, averaging 13.7 minutes, 5.4 points and 2.7 boards per game. For point of reference, in 2013-14, Porzingis (still four months older at the time than Bender) played 14.9 minutes a game and averaged 6.7 points and 2.8 rebounds a game in the Spanish ACB. I certainly wish Bender played more, but let's not pretend it was some kind of huge difference from Porzingis at the same age.
Finally, I think Bender shows a lot of fluidity to his game. He runs the floor about as impressively as you'll ever see for a seven footer, he's a tremendous passer, and he's learning to put the ball on the floor. I'm not sure that he's the right choice, but I think the upside is enticing.