Limiting it to 300ms would probably mean all of Australia couldn't play 
Funny how I never have any problems like you are describing, if the netcode is as bad as you are stating.
http://fs5.directupload.net/images/170703/7ykpbzht.png
That should be enough for Elite. WAY MORE than enough. It's not like I am downloading Battlefield 1 every time I am connecting to a player.
That depends on how close you are to the test server and if it's representative of connecting to a peer mediated by the ED servers which. last time I did a trace route, I was connecting to servers in Ireland.
I have a fiber optic 150/150 connection which will get 0 ping and 150/170 testing to a good local server, but if I speedtest to Ireland I get 150/68 with a 99ms ping time.
Those tests probably aren't doing too many hops. A few month ago I did a traceroute to the AWS server hosting ED and there were several hops to the server with significant delays. I'm not familiar enough with the P2P architecture mediated by the server to know what the impact of the server communication actually is, but my guess is that the weakest link is what causes the performance baseline.
Interesting stuff, but without examining server logs and client logs of all parties in an instance, it's a pretty big puzzle not likely to be sorted out definitively without access to the data.
I found what I could on my end by opening Task Manager/performance Monitor and looking at the connections associated with the ED processes, then pulled the ip address to the server I was connecting to and did the trace.
Fun way to waste time, the AWS server didn't reply to a ping, but I could see the hops involved to route the request and the delays at each hop.
In fairness FDs servers/networking are awful. If i play ED for a day i will drop to menu at least 8 times. To put that into perspective i also play The Division and Killing Floor, i cannot remember the last time i ever disconnected from a server to the menu (meaning it isn't a poor connection on my end).
Really needs bringing in to this century.
Cannot count the amount of times I've nearly run out of fuel because of disconnected several times in a row jumping to the next system, ship swelling the fuel only to end up back in the system i was already in.
None of these things have ever happened to me. If the netcode or servers were THAT bad this sort of thing would be a huge problem.
Host your own instance or play a PvP game that uses dedicated servers. ED very likely won't change its networking architecture.