OK, so let's start with what we know and what we don't know.
Are any of us experts on that pipe and have any of us done any serious R&D on that particular pipe? That's probably a solid NO. So wer are dealing with what we believe to be a probable outcome and that's OK too. We know that typically a collector needs a merge section or mid pipe to stabilize flow and pulses, so chopping off all or most of a mid pipe is likely to hurt performance in some way.
Replacing a can is a simpler issue. The probability that the stock MAC can is dyno tuned and perfect for all engine applications is about the same as my odds of winning the lottery when I don't buy a ticket, but the probability of our new can being any more suited is about the same. We might get lucky. And then again, we might not.
Few of us use all the stock performance and even fewer of us can tell an actual improvement from a hole in the road or in a powerband, so if you like what you want to try, go ahead and give it a go. That pipe is steel and easy to weld bits back on if we don't like the results of our experiments.
Many pipe experiments result in more noise or a dip before it comes on the pipe and both can make a bike feel more powerful even when it's making less power than before. We call it character.
You could measure all the header lengths and work out what length you want them to be and then fabricate a suitable merge collector and transition and appropriate mid and tail pipes and so on, but you may end up having to make a few to test before you get one that really improves performance. For a street bike, go for it, just try to keep it quiet please.