You are such a hypocrite. If you are 250 in England it does not give you a compelling argument to consider yourself an expert at this SPORT unless there are 250 players from England, who are ranked in ITTF.
I guarantee you that a person, who is in top 50 in England is not even close in skill to the one, who is 250. In any sport there are "experts", who can teach the skill very well. They might not even be really good at this sport. Tons of amazing football coaches haven't been that good at football.
Expert in playing (competing) in any sport is the one who can prove not with his ranking but through his match averages against top 50, top 100, top 200 players in a certain sport. As I already mentioned, ranking system is completely flawed, especially for the bottom tier players.
Seriously, you are talking about doctors? Doctors receive very similar in the US (standardized) training and they don't spent 1 year to be an "expert". How about 12 years for cardio surgery? And, yes, all doctors are experts at what they do.
You need to let go of the belief that you own the definition of "expert". Firstly, you've been unable to even define what "expert" means to you. Secondly, others clearly don't agree with you on what "expert" means. There is no universal standard for what constitutes an expert. It's a subjective call. If you think that only the top 50 people worldwide are experts in table tennis, I guess that's fine, but you should perhaps be a bit less hostile about it.
I do find it odd that you say all doctors are experts. This is a strangely liberal application of the term "expert" given that you're so stingy with the term as applied to table tennis. There are 10 thousand medical experts in England but not 250 table tennis experts? It must be damned hard to become a table tennis expert.
At some point, "expert" status necessarily comes down to a subjective and somewhat arbitrary line between players that are very close in skill. Are the top 10 experts? Top 100? Top 1000? If you're comparing to the average Joe, all of these could probably be considered experts. If you're only considering the elite of the elite, then maybe only the top 10 get that classification.
If you look at the NFL, there are almost 1700 players. Obviously these guys cannot all fit into even the top 1000 ranking. Yet all of them are generally considered to be elite players (or they wouldn't retain employment), and they're all being paid over $400K/year for their skills. Arguably, all of these guys are experts at what they do.
Or look at doctors. There are about 300 cardiothoracic surgeons in the US and Canada. You could rank these doctors and come up with a list and arbitrarily say that the top ten are the experts in cardiac surgery. But they are all experts, relative to not only the general population, but to the population of practicing physicians.