Depends on the library, but still a true statement, generally
I've personally never encountered the free version of a library that was actually worth having in the orchestral realm; maybe there would be some percussion libraries. As far as strings, brass and winds go though, I've personally never been impressed with free results. Most paid string libraries actually suck imo.
I will say this though, and keep in mind I own around 5k worth of stuff that I didn't even get on sale and have no intentions of ever buying anything new at this point as I am satisfied with my setup: If you're going to buy samples, you really must evaluate them thoroughly beforehand and aim to get the most bang for your buck. That's why buying a lot of "middle of the road" libraries or cheap things can be a trap that will cost you more money in the end.
I also do not know of anyone putting out professional-quality music who owns just one library or family of libraries; one sample library cannot do everything equally well.
What you have to ask yourself is: How far do you want to take your craft?
If you're interested in Spotify, then presumably you want to attract as many listeners as possible, and if that is the case: NP and Sibelius or free libraries simply will not cut it.
If you want the best presentation of your compositions possible, then there is no way around it: In the absence of a live orchestra, you will have to spend some money (not necessarily 5k) and time learning the art of using high-quality samples and virtual orchestration.
Technology like NP or MuseSounds is advancing rapidly, but still cannot compete with stellar sample mockups.
Lastly, there is another important thing to consider: When I was younger, I used to think it was just hipster nonsense when synth guys and stuff talked about how owning the same gear as everyone else made you sound just like them, but now I see that it is at least half-true.
If you own multiple sample libraries, you will pick and choose instruments and articulations from them and come to favor certain combos that are unique to you, along with your own personal tricks in sequencing and audio processing that will give you a signature sound. For example, I do not know anyone who is using the exact same setup as me, and — at least as far as I can hear — it shows. I don't know of anyone else's mockups who would be mistaken for mine, and that has real value both on a personal and professional level.