...they basically force users to comply to certain process and end-user has very little control to 'customize' the application.
Yes, these systems have evolved over decades. In SAP's case, R3 is a descendant of their mainframe product from the 1970s by way of their client/server R2 in the 1980s. R1 was incredibly innovative back then, and it helped SAP get to where it is today, because they had one of the first production-quality machine independent virtual machines.
Too bad the language was ABAP, aka "German COBOL". But it was the 1970s after all.
In any case the future will be interesting since the value in these systems to the vendor is their proprietariness. The value to the consumer is their automation first and their openness second.
They're all trying to open up and still maintain enough proprietary handcuffs to turn a profit. Their historic margins will fall. They're all going after the SMBs (Small and Medium size Businesses).
All the ERPs but Microsoft will probably end up with increasingly open source components and try to make their profit on services. Give IBM the odds here. But IBM will have to make some strategic purchases first to get to a higher business-level software foundation. (Anyone remember "San Francisco"? Before and After)