You said two different things: (a) avoiding where "two nodes can lead at the same time" and (b) "avoid all situations where two or more leaders exist and produce logs simultaneously".
The verb "lead" there is a little ambiguous, but I think I know what you mean.
In any case, Raft prevents (b) but not (a)...
In other words, it's OK if two nodes *think* that they are leaders at the same time - as long as they can't both actually commit conflicting log entries; this is what the Raft protocol guarantees.
-Archie
Archie L. Cobbs