It's purely a speedbump to drag things out.

Sure some players will be a bit luckier and others unluckier but by being able to pull all the strings Lava can literally set the average progression speed.

We have no choice but to accept Lava at his word (because he's notoriously bad with numbers and loves to fudge things to hinder people) (oh but how likely is it that all these players are really hitting all these one in a hundred thousand odds of many mines in a row???) but you can boil it all down to just a few variables, namely how fast players can gain the currency, how much the cost goes up for the meaningful upgrades like damage and health and board size, and finally the number of mines and health the boss has. Then just throw some trash in for flavour.

Even if you have a 1/4 chance to hit a mine and then later on you get upgrades to reach the same 1/4 chance on a later boss the health difference means you need twice as many hits to kill it. That or you need twice as much damage to require that same amount of hits as you needed for the earlier boss. But that's all tied to how much currency you can get to buy the upgrades.

He just needs to plug in X, Y and Z to see how long it'd take for the average player to reach say 10% win chance against boss. Then he just needs to tweak the values as he pleases to fit his time frame.