Also a CP441-2 may be used for MODBUS RTU, an ET 200S SI-module can also be used for MODBUS.
Physically both networks have a master and slaves, they use both RS 485 as layer. PROFIBUS is much faster then MODBUS, there are 1000's of slaves for PROFIBUS. The PNO have also now PROFINET, that is on ethernet base and working fast on layer 2.
I hope that the answer will help, if you have still questions, don't hesitate to ask me.
All the best, Late
Never say never, think in solutions, not in trouble......