Yes, biggest "issue" with the Marui MP7 that it's scaled to 90% of the real deal (if it bothers you).
I never owned either WE or Marui but I have a VFC and every MP7 has the same issue more or less. Simply that constant bashing to the rear is gonna either crack the receiver or make it to explode whatever inside. Stock backplate is gonna give in over time. To my knowledge there is only one solution: aftermarket cnc'd backplate and any picatinny sling mount around the charging handle to make it more rigid. Well, that's what I did.
I think getting spares for Marui is way more difficult. If I need anything VFC related, I can go to mlemart or wgcshop or any other HK based retailer. Yes, worst case scenario VFC itself but it takes time for sure.