Mechwarriors with their own rides was also a problem for the contract payouts which is why it has changed.
If you are not a fan of that generation method, and some people are not, then you also have the Supplementals which introduces a different way of building a unit. I think Campaign Operations, great in PDF, has the latest version which is more like what is introduced in the Supplementals.
I think the original FM Mercs set in 3055 has a different method as well. The important thing is that for whatever timeframe you want your merc command set up you do your random rolls for mechs/armor/etc on the era appropriate charts. They can be found in books like FM Updates, Shattered Sphere (3059?), Era Reports 3052 and 3062 . . . I think.
One other thing to think about, is that generally the merc generation rules assume you ended up (somehow) with a wad of cash- or at least you and your friends who are starting the unit. It has rules about going into debt as well, and depending on what you try you can definitely go in debt. My unit did not, but I did not pay for upgraded equipment in 3062- my mercs planned to work the Chaos March where they would not face the Clans or even top of the line equipment. My CO's ride was a Battlemaster 1D (his) and I randomly ended up with 3 Watchmen (company assets) in the company funny enough. But having looked through the rules, I found ways to avoid going into debt from the beginning knowing the tradeoffs . . . so my mercs are one of the weird ones- they did not start off in debt. They did go into debt about 4 or 5 missions in to buy a cursed (found out after buying it) Warhammer 7M that had already been modified. The note was held by some bank on Outreach. The starting mech company was half owned and half company bought, had a DS (why I saved cash), had a lance of ASF, some tanks, infantry and a squad of BA. This was after the 'roll for mission' phase where I picked up tanks & infantry along with success.