Not even remotely true, you will spend a lot longer. Number 1: no one drills at the perfect millisecond, Number 2: if you aren't going slow, cheating, or macroing it's impossible to not get some "Nothing here to mine" messages that slow you down, #3 Lag messes everything up so you end up doing a lot of waiting for lag to clear out, #4 There's a finite amount of time to change drilling spots after a rock in completed, and #5 the biggest thing overlooked: your batteries last shorter and shorter amounts of time and you have to leave the mine more and more frequently to buy a battery.
And here's the biggest kicker: Level 0 ~500 gralats and hour, level 50 ~1K gralats and hour, Level 75 ~2K gralats an hour, All that time spent mining (years) just to get to an hourly rate of what a noob doing mushrooms, trash, and mail or pizza can do from day 1. When you think about what you would have gotten if you spent the same time doing mail, mushrooms, and trash or pizza it will be a long time at high levels (>75) before you make back what you could have gotten just doing normal stuff all the time you spent couped up in some mine drilling to get to level 75 and higher. And if you spent that time digging shells and think about what you could have gotten with all those trochus, why would you ever mine?