I like doing both!

Well, from my point of view its because of various reasons, one being to handle players that lower their combat power to use overpowered mechs in lower level matches, and another is because the speed at which a mech can be destroyed can end up being more importand, especially when it comes to long rang combat.

While higher ranked mechs are fun, legendary weapons on bottom tier mechs will still kill as fast as legendary weapons on legandary mechs. As for strategy... some people have it, some don't.