New here, so going to jump into an old discussion. Sorry if bad form.
I competed for a few years back in the mid 00's when I had access to a Decathlon. It was a very positive experience for me. The main benefit was exposure to a flying culture that treated acro as a serious pursuit, as opposed to the biplane barnstorming yahoos I initially learned from. No offense to barnstorming yahoos, but a review of Decathlon fatal accidents on NTSB makes it pretty clear that the primary method of death in an 8KCAB is "hey watch this!"
Everybody in IAC knows someone who has died doing acro or related activities. Consequently there is rigid adherence to safety for things like aircraft airworthiness, parachutes, altitude floors, ground spotters, and progressive skill development.
Competition demands constant improvement. It is generally agreed that an instrument rating makes you a better XC pilot by demanding greater standards of precision. Aerobatic competition makes you a better stick-and-rudder pilot by demanding greater standards of precision in those maneuvers. Someone who spends hours working on recovering spins within 5 degrees of desired heading is going to have more command of their airplane than someone whose idea of a proper loop is "dive, pull and hold."
Another cool part of the IAC is exposure to top level competitors. If you play flag football, they don't let you practice with NFL players, but in the IAC the sportsman and unlimited pilots are all sitting there together in folding chairs watching and talking about flying.
I was never treated as a second class citizen for flying a Decathlon. At my first few contests I was enthusiastically mentored by the contest directors to make sure I was comfortable. Several competitors complimented me on the challenge of flying a bigger aircraft with a slower roll rate, and I think the judges slipped me a few extra points when I flew it well. Some of my friends flying S1T's were a bit irked when I beat them.
I was periodically encouraged by some people to consider a Pitts, not out of disrespect for the Decathlon, but just because that is the natural progression of things in the IAC. The thinking is that Pitts are so hard to fly and land, that if you can master that then you can handle any other plane out there.
Having said that, IAC does have a problem with creeping difficulty in the Sportsman knowns. It was an issue when I was a competitor 15 years ago and it is still an issue, judging from the 2019 known. Multiple vertical uplines clearly disavantage "trainer" class aircraft like the Decathlon against the Pitts. A sharkstooth 8 should be a staple of intermediate, not a sportsman figure.