Speaking about power or distribution panel boards, the manufacturer kit solution has clear adventages. Certified and proven design, saving mounting time… There is no better solution. All he problems you have with them (increase new feeders, for example) are easy to solve if you forsee it in your design.
However, speaking about control panel boards, the kit system is the worst choice you can make. The kit systems are not designed for panels with contactors, control relays, push butons and leds in the front, etc. Can you make it? Of course, but you don’t save time neither money.
So the key is use the kits where they are design for and design the panelboard foreseen the life cycle of the panel.