If you require the entry point to be in the scouted path of a recon team, or a drop point to be targeted to within some short distance of a recon team (and then arrive a couple of turns later), that makes their report and presence more important.
Sure, Col Toda, or most other players with any experience at the game, can design a 50 ton vehicle which will out-perform a 20 ton 'Mech. You can generally do a lot more with customs than with canon designs. The point is, you can carry five 20 ton 'Mechs as cargo, instead of only two of those 50 ton custom vehicles, and the total crew requirements for those vehicles (3 men each) will actually exceed that of the 'Mechs by a man, although the slightly higher tech hour requirements of the extra 'Mechs versus a smaller number of heavier class vehicles will probably even it back out again. The only down side is that you'll need to deploy at least a couple of recon units ('Mechs or vehicles) at the start, for the couple of hours until those "bugs" are unloaded and prepped for action. In that case, a fast Medium 'Mech (like a PXH) probably makes more sense for an initial recon asset, due to its greater survivability and concentration of firepower.
If your only concern is firepower on a flat mapsheet, the vehicles will bring more guns to the table for the transport tonnage and cost. If you're worried about that line of woods blocking hover and wheeled vehicles, hilly terrain dropping all vehicle speeds to a crawl, or a shallow river being a problem for tracked and wheeled, and recon ability is more important than firepower, the 'Mechs are likely to be the better answer in more situations.