I think they knew where they were going with the Solaris rules. Things probably weren't finalized yet, but I'd bet they had a rough idea how it was going to work. I also remember reading something by one of the early Battletech guys, I don't remember if it was an interview in a game magazine or what, but he said that of course FASA made a lot of the canon designs inefficient. That's why they included the mech construction rules, which was everybody's favorite part.
And I also believe that FASA would have purposefully toned down some of the Clan designs. A Loki with Endo-Steel and more armor, and no A-Pods and more heat sinks, would be a terror. Especially against 3025 designs. So they gave it a handicap, like they did a lot of the non-MadCat/Ryoken/Daishi omnis. There's probably also some thinking that "they're the Clans! They do crazy things! Let's just throw some random weapons and equipment in there and not worry about it!"
I either use the Loki like I would use a Rifleman (park his butt in heavy woods at medium-long range and light people up), or without terrain I have him run on a diagonal to keep long range and I snipe. If he's in woods, I am not afraid to go up the heat scale. Lokis are designed to cook. If I'm staying mobile, I'll only shoot 2 PPCs when I know my next move is going to break LOS or that I'm not going to be able to get the full TMM anyway (or if they just give me really easy shots, because screw it, I'm Clan).
It's pretty obvious that there are better designs out there. But it's a lot of fun to take a mech without much armor and just chainsaw your way through a bunch of opponents. With a little bit of luck and the right movement and terrain, a Loki Prime can blow through an entire 3025 lance.