It’s a good question, but it’s also a tough question because there are a LOT of factors as to why someone might or might not want to use a certain plugin. I’ve got a bunch of IK Multimedia plugins so I’ll just try to be fair and say that, subjectively, I think several of them are very good, right up there with some of the upper-tier competition. HOWEVER, more importantly, and after years of owning them, I find I DON’T ACTUALLY USE them very often… and in fact most of my projects don’t have a single one of them. And sometimes I wonder why I even installed them. Take that for what you will, and that might sound very harsh, but stay with me for a moment as I explain a little more…
That’s why this is a tough question because there is SO much subjectivity involved, and also my own preferences, biases, and workflows that I’m used to over many years. And to be frank, I have a massive plugin library. Way too big, and it’s distracting! And now I am planning on downsizing which ones I install. HOWEVER, in all fairness, if ALL I had was IK Multimedia plugins, I’m sure I could make excellent stuff. BUT again, I think we are so fortunate for having so many good plugins these days, that I’d say that about many developers.
So let me put this another way: I suggest you focus on learning all the plugins that come with Cubase first, get used to them, learn your preferences for what is important to you, and over time you’ll figure out where your gaps are and what you might need to fill those gaps.
The plugins that come with Cubase Pro 15 are very good, will take you far, and you really have what you need to make great music already. Steinberg has covered a lot of bases to start out. Your imagination is really the only limitation. DON’T just rush to buy new third-party plugins because they are cheap or on sale or bundled with some big special package, especially if they are older plugins that haven’t been updated/maintained in a while, just because it’s a good deal. But rather, buy plugins deliberately, thoughtfully, with purpose, because you WANT or NEED to use them and you think they will add something valuable to your productions. There will ALWAYS be more DEALS in the future, so don’t feel rushed to get stuff now. And BTW, I wish I followed my own advice in the past, but I ended up buying way more plugins than I needed over many many years. Learn from my mistakes!
Over time you’ll know what you need… and perhaps then you’ll jump in with IK Multimedia OR perhaps not! And maybe you’ll find something else. There are tons of great options out there! So take your time, buy deliberately, focused, with specific results in mind, and you’ll be far better off in the long run.
I know that’s a bit nebulous, but hopefully that helps a little.
Just my two bits. YMMV.