According to Win Values,
his 2008 was worth $14.1 million. Of course, he's been on a steep downward trend since 2006...
See, in baseball, there's more than one month to the season. Yes, he had a fantastic September. He had an okay May and a good July. But the other three months? Well, in April, he was downright putrid. He wasn't much better than that in June, and in August, he was poor.
If you're going to credit him with "carrying them into the playoffs", you need to give him an equal demerit for being ridiculously terrible in April, which is part of the reason why they were in a tight playoff race come September.
Ryan Howard is absolutely not a top-5 player.
Matt Kemp, maybe not, but going forward, he's likely to be better. Brian Roberts? Absolutely. Incredibly underrated player.
Just going through that list, every player on there had an obviously better 2008 than Howard except Prince Fielder, Brandon Phillips, Matt Kemp, and Carl Crawford, and it's razor-thin between him and those guys.
In FanGraph's
Value Wins, he comes in around the 65th spot, tied with Miguel Cabrera and Cristian Guzman. And I know you're going to say "What? Cristian Guzman? Haha what a joke." But when nearly every advanced stat agrees, it's probably time to reevaluate your position. Howard, despite his gaudy HR and RBI totals, was simply not an MVP-caliber player, or remotely close to it, in 2008. He was barely a top-10 first basemen in the MLB, let alone a top 5 player - Pujols, Berkman, Teixeira, Youkilis, Adrian Gonzalez, and Morneau were all better and than it gets really close with Fielder, Cabrera, Delgado, Pena, and Howard.
Thinking that Howard was a top-notch player in 2008 is just living in the Dark Ages where we know nothing about on-base percentage, position, baserunning, or defense. Howard was good at one thing and one thing only in 2008 - hitting home runs.

WHAT? Holy hell. I don't even know how to respond to this. Ted Williams and Ernie Banks never "won anything" either. You know why? Because baseball is a team sport, and TEAMS win, not individual players.
He hasn't produced the runs like Howard has? Once again, are we somehow back in the Dark Ages where RBI's are the only thing that exists? (Funnily enough, in the "Dark Ages" of the 19th century, most people in baseball rejected the RBI statistic).
"Came through in the clutch"? What's "in the clutch" to you? How about with RISP? Teixeira, for his career, has hit .324/.442/.618 in such situations. Howard? .282/.427/.582. Late and close? Tex, .282/.379/.555 to Howard's .247/.394/.521. You're right. He hasn't came through in the clutch like Howard has. He's been better.
Teixeira is Ryan Howard except a switch hitter with excellent contact skills and Gold Glove defense. It's not close who the better player is.