Sometimes the police want bad things.
I won't define it as terrorism, but if you are in the Police and you really have no other legal tool, what do you do? If the boundary is fuzzy enough, they're gonna push for it.
In the end they'll probably have a hard time proving that to a judge, but as a temporary measure they probably think it's useful.
the concern is the "suppress this at any cost" approach.
the heavy sentences can be seen as provocative (13 years for holding an "illegal" election is indefensible. it's pure authoritarian slapdown, reeks of hubris, and spits in the face of actual violent crime convictions. you can get less for murder in Spain!)
this fuels sympathy for a movement that otherwise smelled a bit like the "Piadina" secessionists: a rich region seeking to "unburden" itself of it's poorer compatriot region
such is the unreformed state of spanish nationalism that Madridenses literally will see nothing wrong with extreme civil rights breaches by G.C. etc.
let's not forget that Spain just sold a large order of bombs to Saudi Arabia, so the epiphet "terrorist" is not to be taken seriously, as in the American Gov't etc.
I'm in no way interested in Catalunyan independence, but this posturing by the Spanish Gov't looks RIDICULOUS and should be ridiculed as such.
Also the sentencing was not the harshest by far: rebellion was dropped, state attorney demanded up to 25 years, and “acusación particular” (VOX) was asking to up to 74 years.