Yes it is, and no it isn't. The DOJ is supposed to investigate crimes, gather evidence, and prosecute the party the evidence shows committed the crime. You are 100% on point when you characterized this as "the DOJ going after Trump". It is a corruption of the system for the system to go after anyone, for the focus to be on the person to find something in the legal code they can use. to prosecute.
The Democrats will not be in control of the DOJ forever. The Republicans are not better human beings. If the Democrat controlled DOJ is open about establishing a precedent of secret plea deals hidden in diversion agreements to garner immunity to their friends while hand-picking judges to preside over whatever political operatives could come up with to imprison their political opponents then the Republicans will play be those rules too. That is a very dark path.