I feel like many people underestimate the power of good UX/UI which causes designers (especially freelancers) to be underpaid. Those resources look interesting! I notice many of them are fixed graphics which might be a bit inflexible. For those looking for some more customizable scenes there are libraries like: https://www.drawkit.io/ https://www.humaaans.com/

Just UI alone is underestimated. I have consulted for years. I find that the client's budget and deadline depends almost entirely on the design proposed. One client was 'running low on budget' and after bringing in a designer, he tripled the original budget.

Sometimes not just illustrations, but things like fonts and whitespace matter a lot, and it takes experience to see that you're doing it wrong.

I think good graphics can create a feeling of authenticity so I'm pretty surprised to hear that the watermarks gave that same effect.

High information density works better depending on the context for sure, but in other cases illustrations add to the "human" factor to a brand/site to make it seem more inviting or personal.

Overall, I think the trend has definitely shifted to more of a focus on visual design for clearer communication