I've done straight contract work before through agencies. But that's not surprising in 2019, it's so extremely popular.
I think the agencies play up the "To Hire" part thinking they can get the worker to agree to a much lower rate. If anything, it sounds like your experience is way out of the norm.
I think it's all about pushing for what you expect is fair. Some of what I mentioned was after I negotiated for example (they offered me 17 days PTO, I asked for and got more for example), but nothing that would fall outside what I'd do for any job by asking for more.
As long as you're willing to push for more and stand up for your work / demand better, I don't think contracting is a bad route. I view it exactly as I do a direct hire position... been direct 4.5yrs now and push for more just like I did before this when I was contract at same company. Told them to promote me this past year or else I'd have to search for a better relationship with another company... Jan of this year I got promoted. Same crap, different compensation method
To summarize for OP:
1 - Get all the details up front. Most positions will offer multiple ways to be compensated, and sometimes the same position will be on the market by multiple recruiting companies with different benefits. I've not inquired into one where at least a couple options were not available - 1099, W2, W2 w/benefits (all at different rates). Some can also be salary but I've found it's not as common if you're already US based, it's more for those on work visas. But, I have had straight salary based contracts offered as well.
2 - Don't suck and it is low risk. There is still potential for the project funding your work to be cut, but even in those cases being a good worker will increase your chances of being moved to a funded project at the same company. Also, at my company where we hire tons of agency workers, it also greatly increases your chances of getting a warning ahead of time in the event we know you can't get placed elsewhere and a project is about to end unexpectedly
3 - If you require really solid benefits, it's probably not worth your time. But if you're flexible and view it from an overall dollar value of the compensation, it's very workable and sometimes advantageous. Like I mentioned before, though, you get all these details by asking before even applying. Just don't be shy about asking. I'm sure there are better packages out there than what I've seen, but the one I described that I received is the best I've come across personally. But, I haven't had extensive experience with contracting, just more years than some.