Hi,
I'd like to disagree with some of your numbers
The total you come to for a Shadowhawk is 24 mill. 10 mill for the chassis and upgrades and 14 mill for modules.
1) I have been playing since closed beta. I own a total of 3 weapon modules ... not because I need them but because I thought I would try them out. They don't make enough difference to be worth 3,000,000 cbills each and they are not essential.
2) I have only ever purchased one of any module. It is inconvenient but I simply swap them between mechs ... they are too expensive to purchase more than one.
3) I have only ever purchased one of any XL engine. As with modules, they simply cost too much to be worthwhile buying more than one so I simply swap them (the only reason I have two 300XL is because I bought Sarah's Jenner for a good cause).
Modules and engines are economies of scale ... you only ever buy one. Thus, when you go to get another Shadowhawk you aren't paying 24 mill or even 10 mill ... you are paying about 4.5 mill for the base shadowhawk variants. Since you already bought the engine and some weapons for the first version ... they aren't needed for the next.
So all 3 variants cost about 20 million.
I do think that the double heat sink upgrade could do with a price reduction ... it is used for every mech .. compared to modules, double heat sinks is ridiculously overpowered and is essential for almost any build. Endo and FF are less so but the cost of DHS really does need to be factored into the base cost of a mech.
Assault mechs cost more. Clan mechs cost much much more
However, if you want to drive lights or mediums the investment in grind time is not nearly as bad as your numbers try to portray.
20 mill /100,000 = 200 matches ~= 33 hours of play time (it is probably closer to 7 games/hour than 6 in my experience but I will use 6 since it makes the numbers easier) ... excluding cadet bonuses. It takes somewhere around 60 to 80 matches to reach master on a mech ... so the time spent mastering it is about equal to the amount of cbills you need to get the mechs.
There are a couple of modules that will prove useful but are not essential. Radar deprivation and Advanced Zoom are the ones I most commonly use. Target info and Target decay would probably be the next two ... Target decay is useful for LRM boats mostly ... but none of the modules are absolutely required to have fun with this game. Not having them does not put you at a significant disadvantage. I would rather have someone without modules who can aim on my team than someone with modules who can't
Anyway, PGI has the data on cbill income, MC purchases and the other information required for an informed decision on cbill earnings ... I play casually, have purchased most of my mechs in packs over the last 2 1/2 years (founders, phoenix, one clan pack) ... don't regret it

and make enough cbills by grinding to customize mechs as well as buy the occasional engine, module or new variant. If cbills had been much more plentiful, I suspect I would have spent less. When the game went to open beta I actually spent some MC on standard mechs just to get started. If cbills had been more plentiful I likely would not have done so ... but everyone has different experiences.