Or maybe it's influenced by the fact that when you have a weapon like that, it makes more sense to put him in the position to make a play, or draw coverage off the other pass catchers. Also, what's better, leaving an extra blocker in or making them pay for blitzing by having an open Witten? If the Steelers considered Miller such a weapon, he might have been used more as a weapon.
You're putting absolute statements in my mouth. Obviously the Cowboys use Witten as a pass catcher so much because he's a good pass catcher, because they believe strongly in their quarterback to be able to beat the blitz with a quick read, AND because Witten is a mediocre pass blocking tight end (even experts and websites that rank Witten in the top 3 tight ends in the league right now acknowledge this). Obviously if you have a tight end who is a mediocre pass blocker but an above average pass catcher, you're going to send him out on routes more than you would a more balanced tight end regardless of the scheme. HOWEVER, running 33 routes on 35 passing plays is pretty telling in and of itself.
People clamoring for Heath Miller to be used more in the passing game over the past 5 seasons, excepting 2009 where he actually was used more in the passing game and made the Pro Bowl, has been an even bigger narrative among Steelers fans than the offensive line struggles and the desire to fire Bruce Arians. Do you not notice in every single primetime game the announcers talking about how if the Steelers used him in the passing game more, he would be a household name like certain other tight ends?
It's amusing that you attempt to suggest that because Miller isn't used more in the passing game, it must be because he's not much of a weapon as a tight end. The only thing that even suggests that to be the case, however, is a matter of volume and not quality. I already cited the statistics before. Over the past 5+ seasons, a 72% completion percentage, 11.4 yards per catch (which is 8.2 yards per target, vs. Witten's 8 yards per target), and 45% of his yards coming after the catch.
Here's another stat: he averaged one touchdown per 12.3 catches over that span; one per 17.1 targets. Over his career, he averages a touchdown every 10.4 catches (ESPN doesn't have stats for targets prior to 2006, so I didn't get this stat for his career). Compare that to Witten's one touchdown per 16.7 catches/23.9 targets over the same span, and one touchdown per 17.1 catches for his career.
How you can analyze these stats and seriously try to imply that he wouldn't be a bigger weapon if he would merely be USED more is just bogus.
Witten got his 11.4 as mostly a "safety valve", not on designed plays to Witten. Can we say the same for Millers? Easy to get a nice deep catch in open space (Hello YAC) when no one expects you to be the target, unlike Witten who gets double teams regularly, or is playing in the short zone. Your stats do more to prove an excellent case for Witten.
Okay, so you don't watch Steelers games. Or Cowboys games. Witten gets a lot of quick passes thrown his way, which strongly indicates that he's an early read, does it not? Miller has no more "designed plays" going his way than Witten does, nor a larger percentage when he does run routes. He's also a safety valve...you know, how pretty much all tight ends running backs outside of a few are. Do you really think Witten's 11.4 YPC is more "legitimate" than Millers? And Miller gets YAC because he's fucking big and never gets tackled by the first person. Try watching a game once in a while and see how many yards he gets not simply after the catch, but after contact. VERY rarely is he ever put in positions where he has room to run after the catch. Which wouldn't matter anyway, because speed and agility are not key parts of his game. It's his size and leverage that gets him YAC, not elusiveness or designed plays.
So he didn't get used as a pass catcher due to scheme. Ok. So? That's arguing from silence. He wasn't used and therefore doesn't have the measurable statistics for the argument over time. You are arguing an unprovable hypothetical.
Of course it's provable, but you wouldn't have the patience to wade through the proof. When the line is protecting better, they allow Miller to run more routes or they are more inclined to keep a back in the sidecar. But that simply doesn't happen often enough, or at least it hasn't. The pass blocking actually is starting to look better this year (despite the 8 sacks), but the run blocking of the line is really struggling...
Would you be willing to log into my Game Rewind account and re-watch all of the Steelers' games from last year and see how more frequently Miller is allowed to release from the line when the line is blocking well? Of course not, nor would I expect you to. But of course it leaves you with the easy "you can't prove it" line, even though it's pretty much regarded as the common opinion around the league (ask opposing head coaches about Miller) that Miller would be a deadly weapon if the Steelers could afford to use him less in pass protection.
So when Witten is used as a catcher it's because "he's an average blocker", when Miller is used as a blocker "it's because of scheme". Convenient. Looks like having it both ways to me.
He IS an average pass blocker. This is and has always been his reputation among analysts who actually know about tight ends and blocking. Even Bleacher Report, who ranks Witten 3rd and Miller 8th, notes that Miller is among the best in the league in pass blocking while Witten is average. To deny that Witten's average blocking ability is not a factor in him running 33 routes on 35 passing plays is willful ignorance.
Miller's use in blocking had been of both scheme and necessity, as I already mentioned. Arians loved using 3 tight end sets to block and rarely targeted the backs and ends in the passing game. This is common knowledge.
I don't care if you believe Witten is better than Miller. There are strong arguments to be made for both being better than the other. What I do care about is being scoffed at like an idiotic homer when I present a strong case for my claim. If I were building an NFL team (not a fantasy team), I would choose Miller before Witten as my top tight end. Granted, if that were actually my situation, I would choose Gronkowski (one of the few pass catching tight ends that are truly complete tight ends), but the discussion was between Miller and Witten at tight end.