A lot of blame can be put on the coaching staff and I definitely think they were the wrong group for the job.
But let's go back to 2016... The England team weren't as bad as they are now when EJ took over. They just needed to beef the pack back up.... So they made Hartley captain, bought back a motivated Haskell and were lucky that a bunch of Saracens players were peaking (Billy in particular). It worked for a few years, but the early signs of decay was there even before the 2019 RWC.
Yes, they caught fire and made the final in that tournament. We had a fit Tuilagi playing great rugby, and Underhil/Curry who both kind of came out of no where at the perfect time. I also think we caught a bunch of teams off guard who were not at their best at the time... let's not forget that we looked pretty average for the two previous 6N tournaments. I think the decay started a lot earlier than many of us would like to think. A lot of these players (Itoje, Billy, Farrel etc) were starting to not look like world class players as early as 2018 IMO.
The RWC final shown to us that we were indeed a lot further away than we wanted to believe after beating an OK Australian team (that we were beating all the time anyway) and a NZ team that weren't as good as they had been in the past with a lot of ageing players set to retire.
We then gradually started to decline more and more after the world cup... You could even see it at club level with our biggest teams getting drubbed by European teams. And it has been downhill ever since. We have basically had no good generations coming up through the ranks for a long time... While the likes of France and Ireland have had amazing u20 teams in recent times. Something has gone wrong with our schools and academy system in general... We are simply not producing enough world class quality players and have been leap frogged by our competitors because of that.
Look at the player shortage at key positions. The best tight head prop we've got is probably Kyle Sinkler who can't scrummage to save his life. No decent 12s, no decent enforcers at tight head lock (I am hoping Lewis Chessum can be that guy but alas)... On a positive note, the u18s look pretty good, and their captain who plays hooker looks like he could be the next big thing, time will tell.
We need to definitely change the coaching staff, but it won't solve the generational issues. We need to completely restructure the entire system. The RFU need a complete overhaul and even though it pains me to say it being an active player at grassroots rugby, we need to allocate the grassroots funding to our schools (like Ireland done years ago) if we want the national team to get back to the promise land.