(This is not real esperanto).

The key idea is "passive preposition".
na >> mo (?)
en >> euxn/ mo en.
por >> pouxr/ mo por
etc.

Not that EN is active and MOEN passive, but that between them there is that kind reprocity: if EN is active, EUXN is passive, but if you decide EUXN active, then EN is passive. In the same sense that positivity or negativity of electrical current is a convention. Normally Esperanto has only one member of the pair: EN, DA, EL, POR, PER, PRO, INTER... and the other is to be built: euxn, daux, pouxr etc.

Amazing: MO is the passive of NA (preposition).
MO is able to passivise verbs (movidi) and prepositions (parko moen kuras = A park is place in which people run = A park is run) (and special substantives like PARTO, AVO that are directly related to TUTO, NEPO; so appear MOPARTO, MOAVO).

The passive feature can be expressed diversely at a verb:
Mi naans vidi.
Mi mo vidas.
Mi as mo vidi.
Mi moas vidi.
Mi vidans.
Mi viuxdas.
Mi as vidin.
Mi ans vidi.
Mi as mo vido.
Mi naans vidon.

Also:
Mi estas vidata.

Is AT (or a variant of it) enough to make MO, -UX- and ANS innecessary?

A solution is EJT.
Kind of infinitive AT.

Mi ejtas vidi.
Mi alejtas doni.
Mi ejt vidas.
Mi videjtas.
Mi as videjta.
Mi videjtas.

Parko enejt kuras.