No, that's simply not true - the exemption is if the data needs to be used to actually do the service right now. Quoting the actual directive, "processing is necessary for the performance of a contract to which the data subject is party"; there's no "good service" there, nor future improvements of that service, nor sustained profitable operation of the company. And "necessary" means just that; if you physically can perform the contract without this data, then the data is not legally necessary even if you'd go bankrupt if everyone did that. This exemption covers things like storing your address for deliveries of goods, a messaging app storing your contact info, instagram storing your photos - things where that data is inherently needed to execute that service.
Data can be helpful to improve some recommendations that will make service better in the future - fine, the users can opt-in and some will do that; but that's not an automatic justification to use that data;
Data can be helpful to support the future development your service with revenue - fine, the users can opt-in and some will do that (i.e. many people turn off adblockers and give patreon funding to services they like), but again, that's not going to be legal justification to use data of those who don't want to.
There are a bunch of other exemptions where you can use that data without consent (compliance with other legal requirements, overriding public interest as in e.g. press about public officials), but "I need money to continue operating" is not among them. GDPR is intended to solve the conflict between "I don't want to provide data" vs "I need data-based revenue to continue operating" in the favor of users. If you really do need that data based revenue to operate, then the users can "vote" (by opt-in) whether they consider your continued operation valuable enough to hand over their data voluntarily.