I have always thought that ICOs are the most traditional way of raising capital for long-term projects. As for NFTs, although it generates high profits, it is not sustainable
How high profit that will be generated on NFT depend on the numerous factors. You cna't generalize if that would be sustainable or not because there are lots of things affecting this just like
1. How good the development progress
2. Liquidity and demand in the market
3. Partnership and cooperation
4. Community
5. Market trend and hype
That means if NFT will have good ROI once it can get all of things that can push the hype and the price. NFT project was also doing ICO to raise the funds.
How big ROI depends on how big the community was hyping it. No hype = no gain. People should not expect good ROI from the project that doesn't big hype.