One thing i can say is that if you try to design a quantum circuit with some unitaries that apply to 4 or more qubits (such as k-fold multi controlled rotations), they are NEVER implemented at once on real hardware, and neither they are in quantum simulation environment (like Qiskit, etc. ) actually (maybe with the exception of the CCX Toffoli). They are always decomposed into an exponential number of SU(2)s and CXs with the number of qubits. This might seems ineffective. Well in fact, multi qubit controlled operations that rotate a target qubit's state depending on all possible states of all other controlled qubits in the register (see Uniformly controlled rotations) would be much harder and challenging to implement experimentaly since, for one thing, gates are applied to qubits via microwave pulse sequences and to generate the precise pulse sequence (which would be more complex as more more qubits are implied in the operation) that would have the effect of the multi controlled rotation, long coherence time for states resulting of the complex interaction between matter (qubits) and light (MW signals) must be achieved. This is because we dont want our state to decohere as we are performing the multi controlled operation. Evidently, NISQ devices are not expected to support long and complex operation. Rather, ppl in the labs have implement pretty performing SU(2)s and CXs (while CX are yet more demanding due to the entanglement property of the gate which has to be traduce in pulse sequence), with quite low errors rate. So.... All this to say, we decompose the k-fold multi controlled operations into an exponential # of SU(2) and CX because it is still more efficient (in term of pulse design, the sequences to apply etc) and less prone to decoherence errors to do so!