Yeah, but people have to get the experience on the dance floor somewhere. Not all practicas are necessarily welcoming either - Tangostudent already explained that he didn't have a satisfactory practica locally.
I divide practicas broadly into three categories.
Freewheeling ones where people change partners and mix more easily.
Closed one where people come in couples to practice and it may not be easy to find partners due to gender imbalance
Practicalongas which are more relaxed version of milongas and people are not taking themselves too seriously.
The first two can be either guided or non-guided.
Almost all the local practicas I went to were either lead heavy (with most of the leads being a great deal more experienced than I was) or people brought their own dance partner and didn't rotate. Occasionally I'd luck out and get some dancing in but it was hit or miss and not worth the effort.
Are you in Pacific Northwest?
I have been to practicas like the you described. Those are my least fav ones to go to. I will usually leave them early.
While there I will switch the role. I can follow well enough in practise settings. It gives good sense of what works in leading and what doesn't. It also tells me who are good leaders and who aren't.
I don't go with a practice partner. Unless a couple is practising to compete, I think practising with same partner for two three hours is not best. If I went with a practise partner I would still like to practice with others. I often see that couples who come for practice have mismatch in their skillsets. That means one of the two is spending more time bringing the weaker one upto their level. It is rarer and harder to find someone at a similar level. If you do, then they have to be willing to be a practise partner. Lastly you two should be able to make time for the same practica. That's why those who can practice with different partners will gain more from practica.
If it is guided practica, have the instructor work with you. It is like a 15 minute private lesson for almost no cost. It is best to work on cleaning up one element at a time.