Can't re-size meters in Logic. And Logic is a much more busy interface than the very simple FCP X GUI, so I'd not compare the two. But yeah, not much else you could do, unfortunately. Wider meters would be nice in any case.
Since you have plenty of real estate at that res, you might try adding Level meters to the tracks you need to monitor. There are two actually, and you can resize their windows to 200%.
In the Audio FX section of the Mixer, hold click and add Metering > Level Meter, or Metering > Multimeter (a bit overkill actually except you get a really nice display of 31 bands of the signal plus you can set the "effect" to "hold" peaks).
LPX remembers your scale setting once you make a change and any new meter will automatically be set to that. They're actually quite handy and have a lot more useful information than the Mixer meters.
Incidentally there are new meter calibrations with this release of Logic including EBU & IEC-I/II. The IEC--I seems to have the bast ballistics for multipurpose monitoring of levels. You can also set your peak decay times as well. It's best used with the meters set to Sectional-Linear mode... If I recall correctly
No sign of the K-System yet though, but it could possibly be on its way.
Im running a 5k Retina iMac and generally don't have problems with its metering, they are quite clear, sharp and precise but I am running under Yosemite.
There are a couple of things to try.
First there is the "Thin" and "Wide" settings for the Mixer tracks. Icon upper right of Mixer Window. Try the wide version and you may need to scroll to see all the channels.
Next there are 2 ways to get a Mixer window.
The letter X gets an attached to arrangement mixer, but using "Cmmd+2" gets a separate detached window. I use this mostly and stick on a separate monitor. This is a wider window than when it is attached to the Arrangement area. Again use the "Wide" track setting.
Pulling up on the top will expand vertically to expose all of the controls on the mixer in either case.
Hope this helps, Greg