While paras by and large retains its own mind before evolution and can potentially regain some semblance of independence (such as in the case of paras separating from their mushrooms when exposed to hot, dry environments), the truth is, not really, anonymous. Prior to evolution, the mushroom feeds on paras, which doesn’t necessarily kill them but does actually hinder their growth. Paras that never evolve tend to be weaker and more lethargic as time goes on (more so than most other bug-types, that is), and their life expectancy is less than fifteen years.
However, upon evolution, the host’s mind is completely absorbed by the mushroom, resulting in an organism that’s essentially a mushroom driving an insect body. While this may seem gruesome, the mind of the paras still exists within the complete organism; it’s simply mixed into that of the mushroom. (That is, your parasect can still remember you and everything it experienced with you. It’s simply a mix of mushroom and bug that’s mostly mushroom.) Moreover, because the parasect’s body is essentially that of the fungus, the fungus stops feeding on its host, allowing it to grow in tandem with itself. That is to say, a parasect’s life expectancy is far longer than that of a paras, and it wouldn’t be unusual to have a parasect experience a sudden boost in energy and appetite.
In other words, while it’s true that the parasect host had been taken over and essentially “swallowed” by its mushroom parasite, on the other hand, the act of doing so allows it to live a longer, pain-free life. Meanwhile, it’s true that paras has more independence than its evolved form, but it also is constantly hindered by its own parasitic mushrooms. So … quite honestly, one could argue either way, but I personally think that being taken over by a different species that grants me a boost in energy, special abilities, and a longer life span is a fair trade for a bit of bodily autonomy.
But then again, I’ve also been told I’m odd like that.
The Pokédex According to Bill 