Not only is this not true, it's also not logical. If the Tier 2 system didn't exist, certain individuals would get to the academy 1-2 years earlier than they otherwise would have, but the actual number of students going through the academy wouldn't change. Statistically speaking, at the same time that you were notified of Tier 2, some guy from 1-2 years ago was probably notified that he cleared his Tier 2, so the number of students available never changes. Obviously being Tier 2 sucks, but that's not the reason for missing hiring goals.
Classes tend to run pretty close to max capacity most of the time, and the biggest obstacle is instructor availability. Many of them now are working 1-2 doubles per week or more, which means they're teaching for 17 hours in a day. The job is difficult, thankless, underpaid, and there's just not that many qualified and willing instructors. The new class shrinks the length from 5 weeks to 3 weeks and reduces the number of instructors needed, but almost everyone I've talked to who's taking or taken the CBI class really dislikes it. Obviously this is an attempt to increase the number of students they can train at one time, but if the failure rate in basics goes up, it may not be much of a net improvement in successful graduates.