Correct. The tube boost is good if you need it; G3 users will likely have a fuller pedalboard than G5 users, and be able to add boost/warmth using another box.
IMO, the G3 is the poorly-priced model, now that they've bracketed it with the MS (multistomp single) and the G3x. Either of those, or the G5, is a better value for my tastes. The G3 just fits tight pedalboards better. All 4 are very well designed, which can certainly make for a tricky decision!
Oh, and your pricing looks a bit off. G3 is currently going for $170, G3x for $200, G5 for $300.