The aircraft went UP in a steady climb and came DOWN in an erratic uncontrolled fashion.
Which would be evident WITHOUT FR24 data as the wreckage is now sitting on the ground.
That's actually not correct.
If we
only had the wreckage, then for all we know the pilots might have descended the aircraft controllably for some time (e.g., to attempt an emergency landing with no comm) before an eventual breakup in the air, say at mid-altitudes.
The reason we can surmise that there was something
sudden and catastrophic near cruise altitude is because of the FR24 data, as reflected in the graphs.