Functionally they’re no different. LMDE draws its packages from Debian (probably stable) repos while mainline Mint draws from Ubuntu’s. So yes, Mint will have overall newer packages than LMDE but it’s generally rare for that to affect your ability to get work done unless some new feature you were waiting for gets introduced.
Ubuntu is the Enterprise fork of Debian backed by Canonical, and as such have contributed some controversy into the ecosystem.
Ubuntu leverages Snap packages which are considered ‘bloaty’ and ‘slow’ by a plurality of people with opinions on these matters. They work. Mint incorporates the Snap store into their package management. You might just need to turn it on in the settings.
With mainline Mint you get new base OS packages with Ububtu’s release cycle, and the Snap store.
In the case of LMDE then, you can run a stable base OS on Debian’s rock-solid foundation, their release cycle, and still get your fresh software from the Snap store.
IMO, they’re the same for like 85% of use cases. I find I end up going to extra measures to disable certain Ubuntu-isms on my own systems that run it, effectively reverting it to Debian by another name.
As a student and occasional gamer, the trade off is having a stable base for your learning needs, and still be able to get the latest user desktop apps from Snap.