I'm more of a Beagle Bone person, so I hope you don't mind me answering the question from that standpoint.
The sadness I have about the bone is that it is a means to an end. Purchase bone, insert into host board. Voila, IoT. It gets you to an MVP really fast, but limits your design to that form factor. Migrating away is difficult.
The Arduino, at least, served as training wheels. The end goal was to design an atmega328 into your circuit board, not glue another pcb on top. (Just remembering, there is some progress here with the pocket beagle... Though it does raise supply chain concerns.)
Also unlike the bone, the Arduino opened up a pathway for many other architectures and families of microprocessor, lowering the barrier to entry for 32 bit processors and ARM, keeping the platform relevant.
The bone CPU is getting a little long in the tooth, and there doesn't seem to be a path forward to the next generation of processors in the same SWaP C space. There are others, but the cost or power consumption tripples. The bone is at a real sweet point for price and capabilities. I'd love to see a lower power generation with some fixes to annoying problems (like the RTC).
In their defense, there are two or three orders of magnitude more complexity to an ARM SoC than an 8bit micro. The bone community really is on point with making a stable platform with regular releases, especially given the complexity of supporting a SoC+peripherals with the kernel, device tree, U-Boot, Debian, etc.