Okay, look, I recognise the need for a frontline unit. I still think cloaking our ships would be slightly better, but whatever.
But can we please not deploy slightly-modified humans? That goes against the flavour of the game like nobody's business, and would be harder than deploying aliens besides.
You want medium infantry, do a proper alien. Like this:
Lesser Muton: Despite the unfortunate corruption of our gene banks (or whatever other explanation there is for us not being able to instantly deploy the aliens' usual roster), we still possess the majority of the Muton species' DNA. Rebuilding the original genetic structure would be tricky, but fortunately we can take a short-cut, by splicing in bits of other species' DNA to fill in the gaps. Anything that will fit, really, be it Alien or Earthish in origin.
The result is not quite as impressive as the Mutons we once knew, but it is still a formidable specimen. 7ft tall, intensely muscled, clad in substantial combat armour, what we are calling the Lesser Muton is still expected to be capable of taking a serious beating, thanks to the special bone and muscle structure that protects vital organs and arteries. Their prodigious strength let them wield heavier weaponry than Sectoids and throw grenades further, whilst the genetic memory of their warrior culture instils in them natural tactical proficiency.