Let's say Charm, the natural max for it is 5Y1G, with a bunch of talents to support it, but it maxes out at a point where charming really headstrong adversaries is still difficult. If you're force sensitive you can just keep going, stacking up more force ratings until no opponent can ever resist your charme.
Another thing is actually using force powers. Let's say you wanted to use Influence to inflict strain on someone, with a lot of force dice you could get a very powerful attack cooking, but the rules say defense against the force is an opposed check, and discipline caps out at a place where the big bads in the game can still win. If you use Scathing Tirade + the force however, where it's a standard check that purely counts successes you can shout an entire army into submission with those extra force dice.
This issue is any place in the rule where the force isn't there to activate a power that requires a separate skill check to succeed, but simply adds on top of a skill check. The game just breaks in those places, especially in opposed checks, since even if your target has force dice they don't count in opposed checks. Something that should be risky to do if your opponent has substantial defenses, like rolling coercion on a Black Suns gangster becomes easy.
It's important to remember that Charm, Negotiate, Deception, and Coercion used as skills are not mind control. There is a separate control talent for "Mind Trick" ala "These are not the droids you are looking for." A regular 'social' check still has fall into the area of reason to be allowed. Walking up to the admiral in control of the Coruscant Defense Fleet and trying a deception check of "So, you're not going to believe this, but uh, your entire fleet is to be handed over to the Rebellion." simply isn't going to work. It falls into the category of an impossible check. Same thing with trying to charm the captain of a Star Destroyer into giving you the keys to his ship. At most the check will make him very friendly to you. Maybe you get a new Pen Pal, or maybe he would even let you take a tour of the ship while docked, so he can brag about the new turbolaser targeting computer upgrade to his BFF.
One other aspect to keep in mind, is getting a Force Rating of even 6 would require no fewer than three separate trees, and two of these trees would need to have access to two Force Rating increases. Then you're looking lots of experience to work you way down to the bottom of the various trees to get the various FR talent increases, and of course even more talents that are required to actually be able use all the powerful force using goody-ness.
Final point: Once you do have players that are in the 6 Force Rating realm, they are no longer "another just powerful PC in the Universe". They are the Movers and Shakers of the Universe. They are the leaders of the Black Sun, or the Empire, or the Rebellion. The challenges they face should be crazy epic in scale, and should go beyond a battalion of Stormtroopers.
Edited by Magnus Arcanus