I just went from OEM 2006 rear springs with a 2" block and helper spring to a full custom leaf spring.
The difference is pretty dramatic. More compliance yet still has better weight handling capability. Less noise, the spring is working more than the shackle it sounds like vs. hearing a lot of noise from moving shackles.
Cost of a custom spring is likely more but I think it is well worth it.
I replaced my OEM springs with Aftermarket Replacements. They work way better now... I'm sure custom would work better, but they weren't in the budget or needed timelines. I do have a 1" levelling block on the heavy side so it sits flat. No regrets... Just wish I had an inch or two more height in the front. Once it settles more, I'll reevaluate a front lift.
It is possible to actually have better geometry with a small block then running a higher arc spring. In short it has to do with the roll steer of the rear axle.
Blocks are used by the OEMs even though it would be easy enough to just spec a spring with a higher arc. As far as an OEM application it is simpler and cheaper to have a second part number for a taller spring instead of a set of blocks, different U-bolts, and a more complex assembly build.
But blocks are not perfect. They add leverage to the axle, allow for more axle hop. Not a good thing if you are putting enough HP to the ground to be getting into tire spin (and hop).
I have no fear of a small block. But when the block is the local parts store special, extruded aluminum, taller then it is wide, smaller then the length of the axle spring perch, those I have issues with.
I'm running OEM leafs and 8"/2.5° taper traction blocks on my 2016 F350. Spring wrap is controlled by traction bars. 3/4" U-bolts connects everything together.
These OEM leafs are well match to the capacities i will encounter with the vehicle. Coupled with quality shocks, the ride is very plush. Using the block setup I have allows for the axle to be moved forward or rearward to get the desired wheelbase.
Blocks aren't bad, but stacked blocks are. As they get taller, wrap control will be required, but any leaf spring used with a high torque engine will experience wrap. Even the 5" Deavers I had on my 04 needed wrap control.