Since you have established a rule with your equipment, it is not inherently rude to enforce that rule.
In more detail:
You have proposed a thought out and fair boundary in the sharing of your toys, however, the people you proposed it to are young children who have far more important things to do (such as fire the stomp rocket at their friend) than listen to you and this is perfectly normal. Parents enforcing an established rule will show the kids what is okay or not and although the kids will still likely test the boundaries of the rules, enforcing it should help.
The next question is how do you enforce it? Since we all know that ripping a toy (even your own) out of a random kids hands will probably not go over well. First I would assume the best and try simply asking for it back. Sometimes it will work, but when it inevitably doesn't, I would not press the child; to respect the ways different families work I would enforce your rule through the kids parents and leave it up to them to figure out the best way to deal with their own child.
The other parents have currently been ignoring you when you advise that the children should not play so rough if they want to continue playing with your toy. Here the parents are a bit out of line, their kids are playing with your equipment and they should respect your wishes and make sure that their kids are not too rough with it. However, that does not mean we can not understand why. There are plenty of situations where they know that there is nothing they can easily say that would get their child to be more careful. They know that the next step is for the toy to be removed, but since it hasn't come to that yet they are fine to just ignore it. I think that changing how this interaction goes will result in a different outcome.
My advice is that after you have stated the rule, and then the warning and then asked for the equipment back all to the kids but within ear-shot of the parents, you should then approach the parents and say something along the lines of:
[$Child] is being too rough with my toys, and they are really for my child and his friends anyway. I just asked him/her for [$Toy] back, could you please retrieve it for me?
This is something that they will be far more likely to do, since they know that if they don't, then you will (which is fine for your situation, as their in-action gives permission for your action and doing it with permission is not rude).
There is always the chance that you run into an incredibly annoying parent that will still get upset even after all this. I would not worry, you have done all you can to remain polite and any on-looking parents would be well aware of this.
Lastly, a small plus with this approach is you have a possibility of the domino effect where children might realise that they need to be more careful, and parents might get that little push they needed to reign in their kids. Admittedly a small possibility.