Here, but out of likes sorry. You’re absolutely correct. As long as you have the right kind of light, being under powered usually just ends up creating smaller relatively airy buds. You can literally grow weed from seed to harvest under a couple of cfl’s.
The problem is usually in people that buy a relatively large tent and then an led fixture with s number like 1200 deceptively attaches to it and think they’re gonna grow s pound or two of weed in it. I usually have to be the a-hole that points out it’s not exactly feasible to grow a pound of weed out of a couple hundred dollar setup.
With a few reasonable measures though you can absolutely grow a little bit of weed on a low cost grow though. For a relatively new grower with blurple or an a19 bulb light, it seems the grows that go well usually end up around .5 grams per actual watt of light consumption. There’s lots of variables though, so consider that a rough estimate.
A couple of things that will probably help you out, is definitely keep an eye on your light heights early. The last thing you want is s tall stretched plant. Also, look into some training methods to keep your plant short. Something like a scrog is really good for a low powered light. Or a little bit of early bending will slow the top down a little bit and redirect energy to your lowers giving you a multiple top look. In general just keep your plant from getting too big and swallowing your light and you can be plenty successful.
There’s not a lot of micro growers here to point you towards. But be careful trying to implement some of the things people growing big are going. @MattyBear @raustin @Dieselgrower all come to mind growing pretty damn well in smallish spaces. You can probably follow along their grows and pick up some more advanced defoliation techniques that may help too.