Its true that most players won't have the gameplay hours to compete for leaderboard spots but the leaderboard nevertheless exerts a powerful indirect influence on all of the players that are not on it.
Many people tend to copy leaderboard builds or view the leaderboard as validation that a build really works. We know that Pure Tal Hydra is perfectly capable of dpsing for groups in the GR70 range but you rarely see them in season 4. Builds like this have no visibility on the leaderboard this season and it is difficult to convince others to group with you if you run builds like this.
Another thing is that pugs often have paragon requirements too and whilst they are much lower than the plvls you need to have parity with leaderboard competitors, it is increasing all the time. It is not uncommon now to see P900+ required for 65-68 speeds.
Why is that important? One of the distinguishing features of this season is averaged group exp. 4 player GR speeds with exp% leeches is by far the fastest way to level. Nothing else comes anywhere close. If you want to maintain paragon level parity with at least the demands of pug groups, you have to do a certain amount of 4 player greater rifts per week.
When you lag too far behind, when most groups are asking for p800+ and you are p600 you begin to spend an inordinate amount of time looking for groups or creating groups on top of t8 farming GR keys, on top of farming bounties/t8+ for cube mats.
Everyone is different with respect to how many hours per day they can devote to this game but the kind of plvl requirements in pugs are at the point where new players and late starters trying to catch up will have to devote an...abnormal amount of time to d3.
Thats a choice you make individually. You decide if its worth it (it isn't) but there is no question that botting enables you to devote all of your free time (however much that is) solely to plvling.
Being able to dedicate all of your available game time to greater rift exps is really problematic because it creates an ever growing divide between players who maintain plvl high enough to quickly find groups and those that don't. Those who do get groups level faster and those that don't lag further behind.
This is just an observation I'm having lately. I do not mean to prescribe solutions or to take away from people who like grinding and view their hours played as validation of the the hard work they have put into the game.
The other problem with allowing botters a free pass is how the game is perceived outside of the playerbase. How it is perceived by non d3 players who might be interested in picking up the game. Games like this need large influxes of new players when new content is sold via expansions. More players = more pugs, bigger clans, more people to play diablo with. You do not want this game to be popularly regarded as a joke because pretty soon you won't have anyone left to play with. Why would anyone want to buy into a game they know is a shitsock bot fest?
D2 had a massive reputation for widespread, uncontrollable cheating that made open bnet a wasteland first and then eventually eroded closed bnet too. For a long time, the only people I knew were botters with multiple accounts but none of them actually played the game. So even though D2 appeared to have tonnes of concurrent users logged in and plenty of public games between 2010 and 2012, USEast was a real desolate place 2 months into a new ladder. It could be a real lonely place to spend your free time.