What are the key differences between a MLP with lagged features and a RNN
Let's assume you have 3 features + considering 5 timestamps for each feature. That means you have 15 features as X values.

Machine learning techniques other than RNN can utilize the features as individual columns i.e. 15 columns.

RNN can use these data as 5 arrays containing 3 feature in them. We can feed this 5 array in RNN cell at each time step for a single record. The way RNN cell works when we feed second-time stamp data or subsequent time stamp data it gets processed important information from last time stamps.