Pruned node vs un-pruned node and their ratios on the network

[Itoo]

Can someone help me understand the disadvantages to the network, if any, of running a pruned node, vs a full node?

Also, I would imagine that having more than 50% of the network be full, unpruned nodes would be ideal/sufficient, can anyone elaborate what any actual requirements would be, pertaining to percentage of full, unpruned nodes, to pruned and other types of nodes?
I understand a bit about SPV nodes and their need for full nodes to connect to, and I imagine that a pruned-node would act the part of a full node to SPV clients. Thanks!