Yeah, it very much is a tough row to hoe on either side - and btw, even just adapting to the OOTB package will still cost you a ton of money, and often in ways you didn't expect:
I was loosely associated a few years back with a manufacturing company migrating from their 20 year-old mainframe-based ERP solution to Oracle's ERP. They really had the worst of both worlds, because not only did they have 20 year-old business processes that no one wanted to change, but the whole interface for Oracle was so radically different from the "green screen" 3270 interface of the current system that you couldn't even make Oracle look anything like that. It was doomed to be a complete mess.
But to the point I'd originally planned to make, they tested the system in limited release, and then went live with it for one particular function, which was generating and printing order cards or something like that. What no one had thought of, and didn't occur in testing because it wasn't a real workload was that the old system sent raw text to the printers at the various factory sites, while Oracle (iirc) was generating postscript, complete with logos and formatting, and sending that to the printers at the factories....which it turns out were connected over 128kb/sec links that were promptly swamped by the size of the files.
So the whole project had to be put on hold until all of the links between HQ and the factories could be upgraded, which took months, and the feedback from the userbase was, "What a piece of shit Oracle is, our 20 year old system can print to the factories, why is it so hard for them to do that?!?!"
EDIT: looked back in my notes, 128kb/sec lines, not 512
I was loosely associated a few years back with a manufacturing company migrating from their 20 year-old mainframe-based ERP solution to Oracle's ERP. They really had the worst of both worlds, because not only did they have 20 year-old business processes that no one wanted to change, but the whole interface for Oracle was so radically different from the "green screen" 3270 interface of the current system that you couldn't even make Oracle look anything like that. It was doomed to be a complete mess.
But to the point I'd originally planned to make, they tested the system in limited release, and then went live with it for one particular function, which was generating and printing order cards or something like that. What no one had thought of, and didn't occur in testing because it wasn't a real workload was that the old system sent raw text to the printers at the various factory sites, while Oracle (iirc) was generating postscript, complete with logos and formatting, and sending that to the printers at the factories....which it turns out were connected over 128kb/sec links that were promptly swamped by the size of the files.
So the whole project had to be put on hold until all of the links between HQ and the factories could be upgraded, which took months, and the feedback from the userbase was, "What a piece of shit Oracle is, our 20 year old system can print to the factories, why is it so hard for them to do that?!?!"
EDIT: looked back in my notes, 128kb/sec lines, not 512