[...] the downsides of an open paid beta [...]
We're not even that far yet. The game is still in alpha, afterall. Beta implies all of the main game is implemented and is under testing for bugs, tweaks, adjustments, balancing, and minor feature additions/changes.
As for the EXP thing: yes, it's fast up until you hit the soft level cap (the point where the EXP needed/level starts to sky rocket). My first char hit level 46. It will now take me ~20 Heg Def Fleets, killing ALL ships, to hit 47.
BTW, EXP is tied to fleet point cost. 1 FP = 250XP, for anyone curious. This is the reason why Heg Def and the various Supply fleets are the best things to stalk in the current "late game" (LVL 30 or so and up.) They have the highest base FP cost and are scheduled to appear consistently. (I've started judging my leveling rate as needing "X number of Y type fleets" instead of the raw XP required.) The start of the game levels you fairly well to get you started (Buffalo mk2 is completely living up to its purpose now, ain't it? ^_~) I think once more gameplay is added, the leveling will scale back and slow down once in the mid levels (like starting in the double digits.) On the other hand, it depends on how much content will be in the game and what Alex plans as an average single play session. Most of the JRPG's I've played do about 1 level for every 30 minutes of standard game play (i.e. no purposeful grinding, no avoiding every fight if possible.) They scale back once you hit the intended "end game level" you should be at to beat the game without TOO much difficulty. After that point, you need to find XP bonus multipliers, a hidden dungeon, or something along those lines to efficiently level grind.
Example: ToG:F for PS3 requires you to be either in the post-game bonus dungeon or in the end-game area of the epilogue story arc on MAX difficulty to max your char levels (200 in this game). If you didn't, it takes quite a while to max out. Funny enough, this doesn't take into account maxing your stats and skills, though. That was another, separate system. It ran in parallel to that standard leveling system.
Anyway, the level pacing in the current build is probably on purpose to help test skills: how strong they are, what level featurews should be available at, etc. Alex will probably revamp the skill system at some point for better balancing. Now would be a good time to get feedback on the basic system by letting players access the features quickly (especially without a respec function, so if you want to test out a different build, you need a brand new char to build up.)
It works for what thestate the game is in now. Never forget: the game is still under development and is nowhere near a finished product.