It's not that his points of view are incorrect, that is, Forbidden Lance is indeed a very versatile and useful card; I'm just not entirely sure if using less than the maximum 3 copies of MST would be an optimal choice. This is entirely dependent on the deck one is using of course, HEROes for example, can get by with using 2 copies, since it's not a big deal if a summon is negated or obstructed given the presence of Gemini Spark, Hero Blast, and Miracle Fusion. Given the meta decks nowadays, with the exception of Chaos Dragons themselves, decks like Dino Rabbit, Inzektors, and I suppose Wind Ups, tend to main all 3 copies more often than not. This is obviously to help ensure that a summon or a play goes through (barring something like Evolzar Laggia, Evolzar Dolkka, or Effect Veiler), whereby MST would nuke a potential Solemn Warning or Torrential Tribute, or be chained to the activation of Skill Drain or Fiendish Chain.
The question here is not whether or not Forbidden Lance is an adequate substitute for the 3rd MST, it's whether or not to drop the 3rd MST for something else in the first place, given the current state of the format.
The notion of dropping MST down to 2 would be near 100% valid if you've scoped out your lolcal meta (or the premiere event's meta), and knew for a fact that Chaos Dragons would be heavily represented, maybe even to the point of domination. However, if one takes a general look at the multitude of decks that one could very well expect to encounter at any given tournament, whether it be at a lolcal, regional, or YCS, the odds that you'd face a particular deck many times over aren't particularly high . This is especially the case considering that Chaos Dragons isn't the clear cut best, must-run deck. Against most other decks, barring other notable trap-less exceptions like Frog Monarchs, you are going to want to access those MSTs, and running the maximum 3 copies simply enables you to see it more often. Again, it must be stressed that this is entirely dependent on one's deck: I am fully aware that decks like Final Countdown, for example, have no need for mained Mystical Space Typhoons at all!
As one can observe from the chart above, MST is really only bad against Chaos Dragons. Personally, I feel that it's worth putting oneself at a slight disadvantage against that one matchup via maining more copies of MST, as it's generally good against all the other decks one would expect to contend against in one's ongoing quest to become a master doolist.
I don't know if all this was stating the obvious or not, but I feel that it's worth bringing up, to some extent.