I don't really follow the idea that "midi is lossy" in the sense described. Because it uses note-on/note-off pairs? I don't see the problem there. Certainly the idea that a score somehow has more information in it than a midi recording is ridiculous. A score always requires interpretation. The midi is, in contrast, fully specified, very little room for interpretation.

A midi recording contains pretty precise velocity info for each note (0-127) that is either not present at all in a score, or is present only in the form of a limited number of dynamic markings[1], which govern the flow of dynamics imprecisely, and almost not at all on a per-note basis.

With tempo it is similar to dynamics: midi will precisely determine when notes turn on and off, down to the millisecond, in the process resulting in the midi performance having a precise tempo. In contrast, musical scores have limited means to indicate proper tempo[2], necessitating (as with dynamic markings in a musical score) much interpretation by the musician.

All of this is not to say that a midi performance is somehow "better" than a score. There are good midi recordings and bad ones. A good recording will generally be made by an accomplished musician who in making the recording records fairly precisely a particular (and good) interpretation of the score. Likewise, a bad recording would generally be the result of a poor interpretation of a score. But whatever the case, the midi recording is far more precise than the score itself.

[1] https://www.aboutmusictheory.com/music-dynamics.html

[2] https://en.wikipedia.org/wiki/Tempo#Basic_tempo_markings