Rear Echelon(2.0hp/s) get better repair because they are the weakest of the five engineers, and most US player use vehicle crew anyway.
Sturmpio(3.0hp/s + 1 with minesweeper) get better repair because they take up 9 pop. OKW would be crippled if their engineer repair slow.
Sov and Pio repair at the same rate, 1.6hp/s.
The Sapper(2.0hp/s + 1 with heavy) is really the only one who's repairing too fast.
(although I'm also hoping for a buff to the bren carrier's durability. 200 hp is too low for a combat vehicle).
Actually it makes perfect sense for anvil heavy engies to repair faster.
Otherwise you'd have to spam them only to keep churchills on field.