Here's an idea for how tier 2ish vessels could be placed at the top tiers...
When the Klingon Empire began expanding the Federation knew that it was time to build up the forces. Upon anticipating a need for more short range vessels to accommodate home defense, exploration and patrol, the federation made use of SCE's modulation kits and made smaller vessels quick. As comes with speed though, there is a cost. Many of these vessels could have been shipped with a much better hull, weaponry, and a more experienced crew, had Starfleet enough time. However, time is of the essence and cannon fodder is better than nothing at all.
As of 2409, the Klingon Empire and the United Federation of Planets are at war. But fortunately, the feds seem to be putting up quite the fight. Not only is the federation capable of maintaining a firm defense thanks to their quick start program of introducing smaller, stripped down ships quicker into the hands of Starfleet's most promising lieutenants, but Starfleet is still on the rise. Starfleet is currently monitoring the Romulans, helping rebuild the Cardassian Empire, keeping the Borg at bay, and looking into a possible incursion by the Undine. However, these other missions require more experienced captains. And as the war rages on, lives are lost, promotions are made fast. Some lucky lieutenants have advanced to the role of Rear Admiral and are on the verge of promoting yet again, and their ship of choice is well... what they started out with.
Hence, Starfleet rolled out a program similar to the quick-start in that it used the same modulation kits for these ships, but this time, these ships came reinforced with the latest and greatest, they came packed full of modern weaponry, and they were handled by some of the most experienced crews in Starfleet.
Now, they still might not out-gun the latest and greatest ships of the fleet like the Nomad and the Deverish classes, but these ships would be swifter with their maneuverability. In some cases, a smaller cruiser might have the advantage of the maneuverability of an escort style ship with the addition of the power base and endurance of another cruiser style vessel.
Some of these ships, scouts they might be called could be equiped with better science abilities. Some smaller escorts could have the advantage of the cloaking device in order to ward off the klingons. And perhaps the best part, the Captain, in some cases, particularly in these smaller vessels would have the right to hand-pick his bridge crew, Enemies beware, a bridge full of science officers is a power to be reckoned with.
- that ends my proposal.
I also want to comment that in all reality, the only old ship at a tier 2 level is the Constitution refit. However, it can be argued that that is nothing more than a skin on top of the Excalibur. All of the other classes in the tier 2 levels are all newer than tier 4 levels.
So if the Constitution isn't a re-fit, and a skin instead... whichis more likely than Starfleet busting out an old constitution, then the reality is that all of those ships are actually quite new or at the bare minimum, recent.
Oh yeah, and keep in mind that this is all just figurative. I can't even sell myself on the cloaking device idea. I just think that the argument is there and I want to play around with ways that these ships can be refitted or made to serve the Admiral rank, but for different reasons than the obviously bigger gunned, bigger staffed, and bigger hulled ships of the Rear Admiral tier.