[throwawayish]

As a Qubes user, no, not at all. It's fairly easy to starve other VMs of resources. Qubes is more vulnerable here than other systems, due to it's dynamic allocation of memory. A VM that has a no-matter-what fixed limit of say 2 GB RAM would have a harder time to cause trouble there, but the dynamic management done by Qubes is a major selling point, otherwise it wouldn't be really practical to use on mobile hardware (which is all the rage). I believe one can disable it on a per-VM basis though, so there's that.

[dandelion_lover]

As a Qubes OS user, yes, you can disable the dynamic memory allocation for chosen VMs. So I do not see the problem.

Upd: right click in Qubes Manager, VM settings, Advanced, Include in memory balancing, remove the tick.

And you can even choose how many CPU cores a VM can use.