He realized it was the poor movement profile hampering him. He thought he'd get more mobility out of the unit, given that he didn't have to deal with terrain if so chose. Unfortunately, he also didn't read up on the VTOL rules thoroughly enough and was frustrated when rotor shots dropped three of his four units. And, he also did a lot of side slipping as he skipped over those rules as well.
We're getting more and more players fielding vehicles without going through the rules. We've had a couple of heated discussions with respect to vehicle crits and motive damage.
Well, speaking heresy then, one way you can 'clean up' those discussions, is to run some all-vehicles scenarios with a designated referee holding the book open for those disputes.
Back in BMR days, I used to photocopy sections of the BMR when working a new player in past the introductory all 'mech style of play into combined arms, it was helpful also in that time period, because you could get the entire hit chart for a vehicle on the same sheet with the vehicle record right off the printer-which simplified a great deal of issues for newer or less experienced players, but isn't really practical in the current meta.
OTOH, printing the relevant pages on movement, firing arcs, hit locations and specific unit types into a quicker reference than "Dig through three chapters and sort across a dozen places on the page to find what you're looking for because it was laid out with PDF search function in mind".
But as I was saying, at least have one person who's the designated referee and has the relevant sections for the unit types you're running on hand and available to simplify the argument by showing the goods before people start screaming might be helpful.
at least, until you run into something that has been errata'd, but hasn't been included in the printing you have access to yet.
Quickly and cordially correcting misunderstandings is how you KEEP new players in the community, screaming fights (or snide sarcasm) is how you drive them away.
Some introductory concepts for helping new players master nuanced unit types like VTOLs:
1. Aeroduel. VTOL vs. VTOL, This is to get players used to how movement is different with VTOL units in comparison with other ground units. INCLUDING firing arc limits, and the TMM/AMM (target movement modifier vs attacker movement modifier) as they apply to VTOLs. I recommend not bringing in units with turrets until your players are used to how these handle without them.
2. Stealthy Approach: set up a mission with an NPC and two players, the victory conditions for the two players is to avoid having to make a 'detection roll' by flying too high. Each time they're "Seen" (on a roll of six or higher on 2D6) they lose five points. Enemy kills are worth ten each, and detection rolls happen when the VTOL is 2 or more levels higher than the 'ground level' of the hex they're over at the end of the movement phase.
What this teaches: The use of terrain screening or low level approaches in cluttered terrain. I used to use a 'city map' drawn on acetate over a blank hex-grid 3 maps by 4 maps (or larger). This is another 'hunter/killer' mission type, or 'duel' (though it can be a team sport).
3. The Goat Path scenario: 1 company of light or lighter medium 'mechs, 1 company of VTOLs, maps should be mountainous, not rolling hills, with lots of switchbacks, ledges, long falls and narrow passes intermixed with long range open spaces. The 'mech team needs to get across the map from home edge to far edge with as many units as possible, the VTOL team's job is to inflict damage and casualties (lost arm=5 points, lost leg=20 points, mobility kill=20 points. Each 'mech that makes it to the escape edge is worth 25 points. Team with the most points at the end wins.)
use 'stock' designs as a constraint on both sides, as you can get some outright deranged results with customs.
Each of these scenarios should be played twice using the same starting forces, but switching sides for the players, so that the principles they're supposed to be picking up are what's emphasized, rather than their badass ability to pick min/maxed units or flog BV.
Flogging BV is something that should be saved for after the player's become familiar with the rules governing a given unit type.