autos will not finish in half the time. they stay in veg 2-3 wks then have to go through flowering (at least 6 1/2 wks+ mattering on the strain).
you dont really gain any advantage versus regular beans imo. they just work well for noobies or those who are growing stealth/seriously limited conditions.
You're right that you don't gain much of a TIME advantage in terms of autos from seed vs photoperiod plants from seed. Most of the difference there is going to depend on which strains you're comparing.
If you want the fastest possible buds, the best way to go is to start from clones, which you can literally put right into flowering as soon as they are rooted. Of course you have to generate the clones, but you can do that in parallel with an ongoing grow, so except for the first time you do it, it doesn't cost you extra time.
The advantage of autos vs clones is that during your 7 weeks of flowering, since the auto plants can get up to an extra 12 hours of light per day, they can put on more weight per week. Plus of course, you don't have to generate or maintain clones. If you're only doing an occasional grow and/or prefer to start from seeds each time, that's an advantage.
I've already listed what I think are the biggest advantages of autos: Indoors, if you want to maximize yield out of a small space, they're great for that. Outdoors, they're stealthy, plus you can harvest any time of year. These things don't apply to everyone, but they do apply to a lot of 'personal use' growers, and if so they're really big advantages. If, for example, you live in an apt or highrise, and wanted to put a plant on your deck, an auto would be ideal.
One other auto advantage I didn't mention is that because they are small, and can flower under 20-4 or even 24-0 lighting, if you are running separate veg and flower areas for conventional plants, you can still throw an auto or two in any unused parts of your veg area to get some extra buds.