Experimental mode is meant to be used to test balance changes and their stability in game so we don’t have to wait the majority of a season for simple changes to be tested behind the scenes by a select group of players (this was more a problem in season 1 so there is already clear improvement). It felt like even towards the end when many considered OW1 a dead game the feature was used more than OW2 has done. I only started playing Overwatch a year and a half ago so I know that the ‘dead’ game made use of experimental mode and hotfixes/patches more than the current ‘live’ game did last season by far.
If it is just letting people try out the next patch or season changes having it pre tested for early feedback is important, and if you’re less concerned about it breaking the core game it lets creative changes that could turn out to be actual fixes to in game problems (for example trying enhanced tanks before breaking everything but role queue by their inclusion).
Features in the current live game had been tested for fun in experimental and later added as it can be more fair than it may sound on paper, recent fear of an overpowered Rammatra who turned out to be underpowered for example.
At the least it would be fun to have concurrent experimental patch to play a as a comedic reminder of classic OP on release heroes, giving each character a time to be the Meta (a pretty word for unbalanced characters) without damaging live unranked and ranked gameplay. It was great also when the game is in a balanced state to just see how things could be and if it could be more fun to make certain weak characters more viable.