actually.... pruning is directly related to scalability.  everybody is fixated on tx/s but that is just one measure.  

with many chains there is a bottleneck wrt tx/s, but lets say some public blockchain has nailed it and figured it out, then what?  

now we have 1000's of txs per second which means millions of users and a chain that is swelling much faster than any chain ever has before.

soon the chain is many gigabytes/terabytes.  soon VPNs and even home computer hard drives are just way too small.  people have a choice to shut down their node or spend money and upgrade.  In coins like Bitcoin, these people running nodes are even being rewarded! That all goes to miners.

so quickly the "decentalized" network goes from 1000's of nodes to 100's of nodes to 10's of nodes when it is just too expensive to keep a full record of every tx ever.  

this is why scalability of chain size and possible solutions like pruning or snapshotting come into play and directly are related to scalability. having 10's of nodes trying to serve millions of people with 1000's of tx/s is just asking for the network to run into problems and with that overload on those few remaining servers..... well..... now they aren't doing 1000's of tx/s anymore, if they even manage to stay running.