I've found the opposite to be true--the 5122 is crisper and not as soft as the 4119. I primarily load the 5122 with a Skagit Compact 390 and either 10' poly's in various densities or 10' of T-8. That gets it to bend pretty deep but even then, not as bendy as the 4119. Lines that bring out its stronger/faster aspects are a Scandi Compact 360 and the discontinued Tactical Steelhead 5 (390 grains but still throws a lot like the Scandi in terms of how quickly the rod recovers).I previously owned/fished the Echo DH 4119 and DH 5122.
Both liked Scandi 300gr lines and had very different actions (flex profile).
The DH4119 is a local favorite with stiffer stronger action.
The DH5112 is deeper flexing with a softer action.
Finally got a chance to spend a full day with my Dually 4109 on a few beaches this morning.
Line-wise, I set it up with a RIO Skagit Max Short 325 and a 10' Airflo Salmon/Steelhead poly leader, topped with a foot of 10lb Maxima, followed by about 2 feet of 8lb Maxima. Running line is OPST 40lb.
Flies tossed were a small gurgler, a variation of a Hale Bopp leech with a 1/8 oz bead, small clousers with 5/32 oz eyes and a short (2"-3") bunny leeches.
I landed 6 sea-run cutthroat, ranging from 12 to 17 inches.
In terms of flex profile/stiffness, recovery speed, crispness and backbone/shock absorption when fighting fish, my opinion is that the Dually is an entire world apart from the DECHO 4119. For example, the Dually is:
1) Stiff (relative to the DECHO), bending more in the upper two thirds whereas the DECHO evenly flexes, practically into the butt.
2) Fast and crisp in its delivery, unloading quickly whereas the DECHO is willowy in its loading/unloading.
3) Fights fish with authority whereas the DECHO plays a fish with its flexibility.
4) Is extremely light in the hand and seems to ask for a more athletic stroke whereas the DECHO, when balanced with the right reel, fills your grip with a weight that intuitively communicates the need to take 'er easy and slow down.
5) Appreciates a little more pop from the bottom hand on the forward stroke whereas the DECHO prefers a more even balance between the push and pull of the bottom and top hands.
The Dually seems more akin to the Z-Axis (though lacking the same "feel" as the Z-Axis) than the DECHO. That said, both the Dually 4109 and DECHO 4119 prefer the same grain range (for me, 325-330) and as such occupy the same "class" of rod I'd employ them for, which is sticking fish in the 12 to 20 inch or ~1 to 4 pound range and delivering up to medium weighted flies up to 3 inches long. Neither is by any means a windy day stick, though the Dually may have an edge over the DECHO in this respect, it's not by much. I wouldn't use either in any breeze stiffer than 5-6 MPH unless it's a tailing wind, LOL.
If anyone is looking for a current-production two-hander that's reminiscent of the DECHO's traits, I would suggest you look no further than ECHO's Glass series. Specifically, if you want a rod that's almost exactly like the DH 4119's personality, the Glass 3106 is your stick.
Hope that helps!