Where is this stated? All of the canon images I have ever seen do not show this. Everything I have ever seen shows a very direct comparison to an F14 size wise for a Phoenix Hawk LAM.
A single F-14 wing panel is 7.5m in length and has a chord of 3m at the root. As per
this chart a Commando is 8.5m tall and 4m in width. Which would put the 30-ton Stinger and Wasp LAMs in the 9m tall range in 'Mech mode. That's "nearly as big" enough for me, since none of the "reseen" LAM artwork includes a size chart. The P-hawk LAM is based on the full-scale VF-1 Valkyrie which is dimensionally quite a bit smaller than an F-14 (14.2m long in fighter mode vs 19.1m, with a similar difference in wingspan), and in battroid mode stands about 12m tall, which is in keeping with common medium 'Mechs.
And as for wing loading, proper material selection takes care of that readily.
I don't think you got what I mean by wing loading.
The lift generated by a wing is proportional to the square of the airspeed times the effective lifting area times the air density, as stated in the equation
L=1/2 * p * V^2 * (S * Cl).
When you boil that equation down and solve for weight, the square of the minimum speed needed to fly is proportional to the total weight divided by the total wing area. This is what we call "wing loading" and is expressed in lbs/sqft or kg/m².
A more highly-loaded wing has a higher stall speed and accordingly the aircraft is less maneuverable because to make a turn you have to generate lift equal to the weight of the aircraft times the number of
Gs (extreme examples being the F-104 Starfighter and the Space Shuttle, which were more akin to projectiles than aircraft).
Thus, the more weight you're trying to lift, the more wing you need. Material selection has little to do with it. There is some wiggle room for very thick wings and large slotted flaps that increase the effective wing area, but not enough to put a small wing on a big 'Mech.
In the case of the Wasp LAM, to have the same wing loading as an F-14 (and thus similar flying characteristics, noting also that an F-14 at maximum takeoff weight is quite sluggish and has to burn off a lot of fuel before it can really dogfight) it would need wings 95% the scale of the F-14's (7.125m x 2.85m each). A Phoenix Hawk LAM would need wings 9.6m x 3.8m each, which when folded would be as wide as an Atlas's shoulders and would nearly drag the ground. Even with a pure magic sci-fi wing that produced 3 times the lift because reasons, the wings together would have a volume comparable to the entire center torso.
That's a lot of bulk and ungainly mass compared to jump jets and ASF thrusters, which would be more effective at getting a 'Mech into the air and are well known to be very small in comparison to a 'Mech chassis. A "hovermech" using jet lift would be just as capable if not moreso than a winged LAM, minus having the glide ratio of an office building (not that LAMs do much better when their engines are disabled, going by the few times they appeared in novels).