The problem with grouping people by SP is that SP gain is a linear progression that doesn't necessarily reflect player skill. If you start in the bottom tier, then as you gain SP you're going to eventually be bumped up to the next tier whether you've actually gotten better at the game or not. Your progression would be based on how often you play and whether you use boosters rather than you're actual skill level.

If the tiers are based on K/Dr however, then as you improve your K/Dr will improve and you'll get bumped to the next tier. If it turns out you weren't quite good enough to join that tier yet and you're outmatched then your K/Dr will reflect that and you'll get bumped back down to the lower tier until you can get it back up and keep it up consistently enough to stay in the next tier.

If your reasoning for SP based tiers has to do with access to higher level gear, I believe one of the things CCP already has planned for matchmaking is balancing the meta level between teams.

/me rolls alt, AFKs though BA, still can achieve top score in militia gear and low sp.

The point is that you have to start playing smarter in more than one ways.

First of which is most important is soldier growth. You. Your character, and the equipment you use.
You have to play, you have to learn, and you must learn the hard way. There is no short cut on getting good. Yes you may get ROFLstomped but a 'vet' can get just as steamrolled as easily by superior tactics or unfamiliar opponents.

So in order to do this you have to first observe yourself. Ask the big question," What am I doing wrong?" If you answer low SP and low Gear those are the entirely wrong answer. A militia rifle if used right can down illy prepared heavies in a single reload. Even the best HAV can still fall victim to a militia swarm launcher when used at the opportune time. Maybe you got caught out in the open, maybe you got flanked, maybe you didn't use the right weapon at the right range. Maybe you have the wrong type of modules equipped. There are dozens of things you can constantly improve upon yourself as a soldier and unless you play you won't ever find out your own flaws and which flaws you are most willing to live with.

From there you then need to train up your sense of battlefielding. Amongst which includes the all important ability to observe and be aware. Know what the enemy is up to, what they have deployed, and tactics they're using, why is all of those combined very effective? More chances or not had you put those same guys that rofl stomped you into the ground you would still been roflstomped had they been in militia gear. Practice what they do see how it works for yourself.

As for the earlier comment about grouping people by SP, I am what you call an Omni-solider, I have specced into just about everything at once, so overall where most people would have gotten 1 or 2 prototype fits fully loaded I have 0 Advanced grade fits across the board. But I have quite a few fits nonetheless and hold my ground well against prototype players. The game should be shifting matchmaking sooner to hopefully more skill base and stray away from random encounters as it is now.