I've always wondered how a system with an exponential rate of packet transmission could be called "slow start". Then I saw Figure 3 ("Startup behavior of TCP without Slow-start") from Congestion Avoidance and Control. This congestion-control-free TCP sends as many packets as possible, resulting in huge amounts of packet loss. The graph shows a sequence of sharp saw teeth. In the trace, one sequence packets was resent four times!
With TCP Tahoe, on the other hand, the trace showed a smooth increase and a steady rate of delivery with few retransmissions. Overall, the TCP with congestion control transmitted data at more than twice the rate because it didn't wastefully retransmit packets. Compared to a near-vertical line with sharp slope, an exponential plot really does look slow. I am now at peace with the name "slow start".