Everyone kind of has their own thing going on in this regard; some people use a lot of presets and spend most of their time composing and songwriting, while others like me do all of their own designing all the time and should probably study theory and composition a little more in order to expand themselves in other directions.
Personally, I like to work the muscality into my designs but you could technically just make a bunch of your own patches in Serum and Vital and that would be considered sound designing by a lot of people as it is. I’m sure a lot of really great designers haven’t even opened PD or Max in their entire lives, but it all depends on how deep somebody wants to go with it.
One last thing to mention is that mixing can be its own ballgame entirely; you could be making awesome designs but really poor EQ and compression choices and easily ruining your entire sound in the process. Most of the time, beginners overcompensate by adding a bunch of EQ curves and really overkill compression to shit that doesn’t need it, so that’s a thing. I also did this for way longer than most people, and most of the mistakes I’m pointing out are coming from years and years of personal fuck-ups.
Also, personal taste is personal. Some people will literally listen to someone’s 45-minute, 1-track, paulstretched dark ambient album and completely gloss over shit that you put massive amounts of hours into. Life is like that, but if you’re truly happy with your own output and know what you need to expand on, then you’re probably pretty self-aware about the process. Design / composing / songwriting / mixing can all be jumbled up in various ways together, almost to the point where you don’t know where one starts or another one ends, and that’s the beauty of it IMO.