As a regular transit user, intuitively I would not regard Finch LRT as rapid transit.
And yet, it will be a helpful line: faster than the bus, protected from traffic congestion, and having higher capacity / more spacious vehicles. Not every transit line has to be rapid in order to be useful.
Term "rapid" is vague and means different things for different people. Intuitively, I feel like calling a transit line "rapid" if it is:
a) Fully grade separated, or
b) Has a sizeable fully grade-separated section, and the rest of it is in street-median but not in mixed traffic.
Based on that, subways and GO lines are obviously rapid. Eglinton LRT will be rapid transit too, because of the sizeable central section in the tunnel.
Finch LRT will not be rapid because it has no sizeable fully grade-separated sections, but it will be useful nevertheless.