While success isn't always about spending big I'm sure the Ryanbirdios excellent piece on goals conceded would also show that the overwhelming majority of those teams were top 3 budget as well .
And also very likely to be the top scorers too!
You can look through a season and find games where conceding 5 fewer goals could have given an extra 10 points, but the exact same argument can be made for scoring 5 more.
Peterborough and Hull, top goal scorers this season. Rotherham last season. Luton (1st) Barnsley (3rd) season before. Wigan and Blackburn 1st and 2nd. Sheffield United (1st) Bolton (5th).
The reality is that to succeed at any level you need a strong defence, an effective strike force and often goals throughout the team, a highly competitive budget and a bit of luck with injuries.
This season, our defence was pretty good. Stevens, Long, Atkinson, Moore and Ruffels are comparable with most league 1 defences. The problem was that we often lost midfield battles, didn't defend as a team, especially down the flanks, and weren't strong enough mentally to close out crucial 10 minutes spells.
Also our goal scoring was pretty good. Taylor with 19, plenty from the defence, set pieces, wider players.
Where we struggled in both is through the middle of the pitch. Gorrin, Brannagan, McGuane, Kelly, Forde, Hanson all struggled to ever really control games, gave little defensive cover, and only scored a penalty and penalty rebound between them.
We saw some lovely touches from McGuane, and Brannagan had looked much better in the run up to the playoffs. But the former had Kelly and Gorrin alongside in a battling but fairly negative midfield, and the latter had Henry and Sykes in a weak but attacking middle 3.
We need to get that midfield working more effectively. We need to look at the transition between defence and attack (and Kelly was actually pretty good at this!) We need to move the ball quickly into the wingers to run on to rather than give it to them at a standing start on the halfway line. We need to know when to thread a ball through to Taylor like Barker should have done at the end of his early run last Tuesday. And crucially, we need to find a way to do all of this when teams press high or give us little space.
Get that right and we have the foundations or a very good league 1 side.