when the fuel consumption is worse than much powerful (1.8 CVT-i) and bigger (1.6 auto and 1.8 cvt-i) then yes a car is certainly underpowered.
under normal driving 1.8 cvt-i gives 10-10.5 and 1.3 gives 8.5-9,
under heavy footed driving altis falls to 9.3 and the worst figure that I saw was 8.6 when driving like a maniac during break in while demanding even slightly more power can send 1.3 auto into 7ish figures, even sa 6.7 kmpl once.
Last under light footed (eco light on during 40-50% of the time) driving I haven't seen more than 9.5 on gli auto but 10.5-11 is easily possible on Altis 1.8 and when one tries to keep it in eco zone during more than 70% of the time the average can go upto 14 kmpl.
I've noted these figures during various trips with friends in past year and fuel expenses were also shared accordingly. 
Also I forgot to mention about the cars I'm talking about, Gli 1.3 auto is on original rims and tyres while Altis 1.8 is on 17" Vossen replica with 225s all around still altis is giving better economy also the actual travelled distance is more with larger rims due to odo not being calibrated for it.
