A contemporary (to the exit) account certainly thought Trello underperformed, business model wise (was very complimentary of the tech stack, though)[1]. I've never worked in the B2C space so I can't comment on whether freemium was a better option, but I did spend a few years in B2B/SMB SaaS space and the business I worked for looked very different from Trello and was more successful, financially (our tech stack was almost certainly worse).

[1]: https://usefyi.com/trello-history/