You're not going to get a complete picture of Horford's value by looking simply at points and rebounds.
I'm looking at the decline. If you ignore the decline, you ain't doing it right.
As for the value... Horford is what he is, an injury-prone big with diminishing ability who will command a massive payday this summer based on past performance.
I recognize the concern re: decline, but I think this is a case -- much like Kevin Love -- where it's hard to distinguish decline from change in role. I tend to think there's probably a little bit of both going on.
Anyway, decline in points and rebounds is concerning, but Horford's impact goes beyond the box score. Adding a versatile, experienced two-way guy like that in Brad Stevens' system could be huge.
Horford also has the kind of skillset that suggests he ought to be able to remain a valuable player well into his 30s, even if his raw box score numbers don't blow you away, much like David West or Luis Scola.
Regarding injuires, hasn't Horford been relatively healthy his whole career except for two major pectoral injuries? I seem to recall that's what kept him out for the majority of two of the last five seasons. I would only re-sign him if I felt, based on what the doctors told me, that the pectoral issues weren't likely to resurface in a major way.
I acknowledge Kozlodev's point about injuries and decline in stats. I also acknoeldge your argument about change in role. I think the reality is somewhere in the middle.
Looking at Horford's usage rate, it has dropped reasonably significantly over the past two years (from 24.7% to 22.2% to 21%) which pretty safely explains his drop in scoring.
It doesn't explain his significant drop in FG% over that stretch, but that can be explained (at least this year) by the fact that he has increase his three point attempts by about 600% (from 0.5 per game to 3 per game). That's naturally going to bring down your FG% overall, so that's fair.
If you look at his shooting percentages from everywhere else on the floor (including in the paint and from midrange) they are pretty much up where they have always been, so I'm confidently convinced that his offensive talent hasn't dropped off significantly due to decline in skill/talent.
However, one thing that does concern me is the drop in Free Throw Rate. Horford's career FTR is 22.7% which is pretty medicre by any standards, and that's about where it was three years ago when his usage rate was at it's peak. Last year his FTR dropped to 14.6%, and this year it dropped again to 12.8%...and they are shockingly bad numbers for a big man who is quite skilled at scoring in the paint.
You'd think more three point attempts might explain the reduced FTR but it doesn't, because last year he only attempted 0.5 3PA per game and his 14.6% FTR was (by far) a career low. It suggests he's becoming less explosive and/or aggressive in taking it to the basket.
This doesn't concern me in a huge way because Horford it's been years since Horford was competent at drawing fouls, and he's efficient enough everywhere else to make it a non-concern, but it does suggest that there might be some physical decline taking place forcing him to play the game a little more soft.
The drop in rebounds concerns me a bit more. Usage rate shouldn't really affect his rebounding, so seeing his rebounding drop from 9.9 REB/36 to 9.2 REB/36 to 8/4 REB/36 to 7.8 REB/36 over the past four seasons concerns me a bit.
Horford also is not a quality rim protector. He's not a terrible one, either - he's about average to be honest.
Rebounding, getting to the line and protecting the basket are three things we don't do that well overall, and the fact that Horford doesn't help (or in two cases, actually hurts) us in those areas does concern me a bit.
It basically means that we MUST find ourselves a quality rebounding and rim protector to put next to him, which in turn limits what guys we can play him alongside. Amir Johnson should fit well, but that's about it.
Still I am content enough starting with Horford for now, and then looking for that second guy later. At the very least Horford is a good locker room guy with a veteran presence who
will help us. I'm not convinced that he's worth a max deal (especially under the rising cap) and I don't think that he's a game changer on his own - but he's a solid vet who could make an impact for us this year, and for another 3 or 4 years after that probably.