deftype is 6 times slower than vectors?

slow-deftypes.clj

(ns deftypes.are.slow
  (:use criterium.core))

(deftype Pair [a b])

(bench
 (->> (range 100000)
      (map #(vector % (inc %)))
      (map second)
      (apply +)))
;; WARNING: Final GC required 5.277774812522496 % of runtime                                                                                                                                                                            
;; Evaluation count : 1200 in 60 samples of 20 calls.                                                                                                                                                                                   
;;              Execution time mean : 45.895915 ms                                                                                                                                                                                      
;;     Execution time std-deviation : 1.654094 ms                                                                                                                                                                                       
;;    Execution time lower quantile : 43.937738 ms ( 2.5%)                                                                                                                                                                              
;;    Execution time upper quantile : 49.875242 ms (97.5%)                                                                                                                                                                              
;;                    Overhead used : 13.796370 ns                                                                                                                                                                                      
;;                                                                                                                                                                                                                                      
;; Found 2 outliers in 60 samples (3.3333 %)                                                                                                                                                                                            
;;  low-severe   2 (3.3333 %)                                                                                                                                                                                                           
;;  Variance from outliers : 22.2418 % Variance is moderately inflated by outliers                                                                                                                                                      

(bench
 (->> (range 100000)
      (map #(Pair. % (inc %)))
      (map #(.b %))
      (apply +)))

;; Evaluation count : 240 in 60 samples of 4 calls.                                                                                                                                                                                     
;;              Execution time mean : 285.409938 ms                                                                                                                                                                                     
;;     Execution time std-deviation : 17.054052 ms                                                                                                                                                                                      
;;    Execution time lower quantile : 267.066433 ms ( 2.5%)                                                                                                                                                                             
;;    Execution time upper quantile : 326.247203 ms (97.5%)                                                                                                                                                                             
;;                    Overhead used : 13.796370 ns                                                                                                                                                                                      
;;                                                                                                                                                                                                                                      
;; Found 6 outliers in 60 samples (10.0000 %)                                                                                                                                                                                           
;;  low-severe   4 (6.6667 %)                                                                                                                                                                                                           
;;  low-mild   2 (3.3333 %)                                                                                                                                                                                                             
;;  Variance from outliers : 45.0782 % Variance is moderately inflated by outliers      

For posterity: the issue is reflection on line 26.