Hey, I played the original Mechwarrior
in a Let's Play thread from a while back but unfortunately, all the images which I had hosted on Imageshack are gone, so it's pretty much unreadable. Anyway, the deal with that one story wise was that there was a main story line, and you could find story-related missions, but you were free to fly from planet to planet and take mercenary contracts from any house, which is what you would spend nearly all your time doing. Along the way you would hire mechwarriors and buy/salvage/customize/sell mechs for your Lance. Difficulty progression came mostly in the form of more difficult contracts being available to you as your reputation with different houses increased. The missions were very simple though, I think every single one was just your mech(s) starting at the opposite side of a rectangular area from the enemy mech(s), and there might be buildings on one side or the other that you could attack/defend.
It's worth noting that in MW1 and every other Mechwarrior game, mech weight classes served mainly as a form of progression. More mech was nearly always better. Sometimes you had weight limits for the dropship, which prevented you from being totally overpowered for missions, and there are like one or two 'stealth' missions where you're required to go alone in a light mech, but the biggest mechs were always the best, and you spent your career working your way up to them. In Solaris, the gladiator arena, matches are done by weight class, so the Amateur championship is limited to Light mechs, then the Intermediate one is limited to Medium mechs (or you COULD bring a light mech but you never would), etc. Anyway, you get the idea, Assaults cost more and are better. In Multiplayer, you would have one or two guys on your team play Light if it was a capture the flag match but otherwise you would take the biggest mech within some agreed-upon limit.
Oh yeah, Multiplayer in the Mechwarrior games before MWO was much more like a slow stompy Unreal than the World of Tanks-inspired stuff we have today. There was Capture the Flag, Deathmatch, Team Deathmatch (all with respawns) and Battle Royale/Team Battle Royale, might have been a different name, which was one-life and saw a brief attempt at being made a 'competitive e-sport' of sorts on G4 TV (lol remember that?)
So, the idea of different weight classes forming a specialized role is pretty much unique to MWO, and it works very well for that type of multiplayer arena game but it's not typically what one would expect of Mechwarrior. As others have said, they made the game very different from other Mechwarrior games to create that ecosystem, it's not consistent with the gameplay or fluff of any other Mechwarrior stuff. I can't say whether they'll try to keep the balance more similar to MWO than the normal mechwarrior games, though.
Also, in the interview they said they were considering not letting the player make their own mech loadouts, which makes me sad. They say that mechs within various weight classes in MWO feel 'samey' but I think that's only because they come with so many different hardpoint variants. Mechwarrior 4 had a good variety of mechs and most of them didn't feel redundant because they all had unique combinations of hardpoints.