If by "basically all do the same thing" you mean they all detect metal, then yes, that's true. But they most certainly do not all do the same thing and some are in fact very specialized.
As I've stated earlier, they all pretty much detect to about the same depth regardless of brand, model, or cost. But that's only in ideal situations which are rare out in the field.
With a basic detector you'll also either end up digging a very large percentage of iron junk compared to good targets, or miss the good targets altogether. That's fine if that's all you want -- some people are actually looking for iron. But be prepared to also dig up hot rocks, bottlecaps, etc., which can be more easily avoided with advanced detectors, although no detector can eliminate them completely.
More advanced machines will detect objects that simpler ones can't, even if the object is only an inch or two under the surface, unless as I've said above you don't mind digging every single signal you get and hope there's something good alongside whatever trash you actually detected.
Even the more advanced detectors can be simply removed from the box, turned on, and find metal without any understanding at all about all the options and customizations. They all come with preset basic programs. And they would still be better than the basic detectors at discriminating between good and bad targets even right out of the box, but wouldn't be worth the price if you don't intend to utilize its programing to its full potential. An intermediate detector would be your best bet in this case.
Back to depth, only very large targets can be detected at two to three feet. There's a YouTube video of Gary Blackwell digging a steel truck wheel at a measured depth of three feet using a Deus. Not exactly something I'd want to do but it does show what kind of depth is possible with large objects.
As far as the weight of high-end models, the original XP Deus is one of the lightest detectors you can buy at about two pounds so weight isn't necessarily an issue with high-end machines.
But reality is we all want something we're comfortable with using, otherwise it will end up sitting in the closest or listed on Craigslist. We each have our own criteria for what exactly that is.
