The restriction is enforced by the size of your wallet, plain and simple.
Every player will be able to buy what they can afford, regardless if they earned the money themselves or others pooled their money on them.

Edit: Typo

... and started building the big ass 'Mechs like crazy to have something against clans omnis

If the map is build to give the lighter ones an advantage I am sure you will see them more than the heavy ones.

Not to mention battlefield roles and map size coming into play.  The lighter, faster 'mechs will definitely be a big part of the roster of any intelligent commander.  Think back to playing capture the flag in Mech 4.  You had lights to serve as flag runners, assaults to act as base defense, heavys for long range support and fast mediums for mid field domination.   That's the simplest example of 'mechs playing their roles, but it really made the lights the stars of the show.

In MWLL, you are going to have ground vehicle assets, aerotech, the c-bill system, and VERY LARGE MAPS.  http://www.mechlivinglegends.net/component/option,com_smf/Itemid,36/topic,2049.0/

Each of these will provide opportunities for the Ullers, Cougars, and Pumas to shine.  And if that doesn't float you boat, consider well coordinated 8 'mech swarm attacks against the slow moving big boys.  Boy this game is going to be fun.

We're actually working on something to prevent abuse of the cash system. We hope to see the practical use - or lack of it - in the beta tests.

Most Battlemechs are infact Medium Mechs, Assault Class mechs are still relatively uncommon with Heavy and Lights in larger numbers (with light being more commen of the two).

The medium mech is the workhorse of the house forces even during the later time lines.
Though House Steiner will allways be known for it's use of large numbers of heavy and assault mechs.


Basic house mech doctrines (3050+ era)
Federated Suns (House Davion)
Prefers mobile calvery style tactics, most of their mechs are at lest 5/8 (85kph), they also favor Lasers and Autocannons. They do have a powerfull contingent of "slower" assault mechs.

House Marik (Free Worlds league)
Smiler to House Davion but favors more of a running battle and Long range weapons like LRMs and light gauss rifles, only to Finnish off weakend units with lasers and SRMs.

House Steiner  (Lyran Alliance)
Walls of Steel, the lyrans preferr a slow set piece assault mounting Gauss rifles, heavy autocannons and ERPPCs. Though they favor assault mechs they do have good quality light and medium mechs (for that calvery role).

House Kurita (Draconis Combine)
The Combine have undergone a rather dramatic change over the years, they went from one on one duels and swarms of light and medium mechs, to a more balanced force both weight wise and tactically. The current DC forces favor C3 systems and PPCs, with lighter mechs acting as the spotters for there heaver brothers allowing them to hit with uncanny accuracy. They have also a very mobile force.

House Laio (Capellan Confederation)
Minefields, minefields and more minefields the capellans love a good ambush, they also prefer long range weapons. Mechs are fairly mobile so that they can close with the enemy once the ambush is sprung.

This and more can be found here
http://www.classicbattletech.com/forums/index.php/topic,34318.0/all.html

I hope the price difference in this game also justifies the effectiveness. Whereas in Mechwarrior 4 there was like 30% price difference between light and heavy mechs. Thats an easy choice if you ask me.