I suspect this very much depends on how much you use it… and how…
its a deep module, so like others it pays to really sit down and use it regularly, and initially try to use every single module.
i think if you have a ‘casual’ use of it, where you pick it up every now and then and load up a few preset and modify them a little - I think it will take a very long time to learn.
on the other hand, if you always develop patches from scratch - and try different things - I think you can learn pretty quickly. (albeit, it may be a little frustrating intially… as lots to learn)
but, of course, that requires a time investment, and also the motivation - which of course can vary from one person to another… e.g. if the you have a huge eurorack, with lots of modules - perhaps its hard to focus on the SSP - whereas, if you have a small rack, and its very important part of it … then you’re likely to spend more time with it.
so Id not ‘beat yourself up’ about it, its quite natural for it to be different for different users.
Personally, I think the concepts are very straightforward, once you have done a few patches - it becomes quick and pretty natural… and its easy to see when you ‘forget’ something (e.g. opening an input) - the scopes are vital for this.
More ‘difficult’ is knowing which modules to use, and how, and when and for what.
There is no getting around the fact, that a ‘virtual modular’ is more deliberate than patching physical modules - so that means knowing whats available…
I guess the other side is experimentation - on one hand, I often think deliberately about a patch I want to create and figure out how to do it, but if I hit stumbling blocks or limitations - I let that deflect me into doing some slightly , or very different.
I think this helps since it stops frustration setting in, when you cannot seem to quite do what you want to do.
In other words, it becomes more ‘What can I do with the modules/feature I have?’ - rather than, 'why can’t I … ?"
Only you know if you have invested the amount of effort you are willing to invest.
The questions I ask myself in these situations is simple…
when I got the module what did I want to DO with it? is this possible? if not why not?
is there another use that makes it worthwhile?
what do I use if for?
at the end of the day, it doesn’t matter what the ‘dream’ was, of what it would achieve,
that dream always has to turn into a reality.
but again… easier said than done 
anything is possible…
as the code is not open source, the factory modules and main UI (network/recorder) cannot be change by anyone other than percussa - so its a matter of talking to them.
generally coding is often not about ‘difficulty’ , assuming you have skilled programmers, rather its about time and resources - at the end of the day, coders need to eat and drink too 
as I said, I dont personally find any issues with the main UI - though for sure there are some quirks with different modules.
some of that though is down to ‘history’ e.g. different users requesting different features, and trying to accomadate everyone - that can be pretty tricky. its also difficult to ‘fix’, since it may involve breaking peoples patches (which some users will be fine with, others not so much)
anyway, the above is very personal - and I recognise, Ive likely a different take than others.
as I mentioned on my video on how I use the SSP, I try to use it in a pretty ‘adhoc’ way - partly because I want to retain that ‘modular’ feel, of starting from scratch.
btw: Ive still got a ton to learn, and experiment with on the SSP.
I really want to sort out my samples on the SSP, form a kind of sample library. also I want to improve the workflow I have with the SSP and thinks like the QuBit Nebulae/Octatrack
… and I really need to dig into the using it more for complex fx… which was my original goal for the SSP when I bought it.