well yes different receptors and all sorts of processes are implicated in psychedelic effects
even though 5-ht2a does not explain all, I think its pretty clear it is a main component or pathway for the effects, due to the fact that when 5-ht2a antagonist (ketaserin was the case I think) is administered, the psychedelic effect is blocked.
I always imagine the neurotransmitters and receptors as the trucks and roads or tunnels through which 'stuff' gets transported. But talking about the trucks or the tunnel bears no significance for what the truck is carrying, which is much more dynamic.
So if for example the truck carrying food for a town does not reach the destination because the tunnel on the way is blocked (by ketaserin, for example), and then people start starving, then one could say: 'see, this truck and tunnel are responsible for those people's digestion. But then if the tunnel is liberated, and another truck passes, this time carrying toys, and then one could suppose that now the people are gonna start eating, but no, it doesnt happen as predicted, the truck did pass in that exact place but it had nothing to do with digestion, it was toys for the kids (like when this lisuride goes to 5ht2a but does not have hallucinogenic properties)
It seems to me that even though neuro transmitters and receptors are very interesting to study, they are still a VERY crude way of looking at things. The brain is so complex and full of these microtubules and microfilaments, and all this flow of electro magnetic patterns, blood flow, and in general a very complex organization, that looking at one thing at once can never explain the whole story.
I dont think we are going to 'catch' so soon the exact workings of the brain, and the why and how each substance works in the brain.
am I making any sense?