Life differs as a creep. Instead of starting against level 1 rats that have no chance of killing you, you start against level 50 freeps, any of which can kill you. And yet kill them you must, because your only way to advance as a creep is through infamy, from defeating players. You have all your basic skills at rank 3, start getting racial toys at rank 5, and are about equal to a level 50 freep at rank 7. (Unless it is a Burglar, who you can only beat one-on-one if you are rank 7+ and he is lousy, poorly equipped, drunk, and AFK.) And then the freeps can add raid gear and consumable buffs.
An odd thing is that some abilities seem to be balanced for the long-term. If a rank 0 skill has a rank 2 upgrade, you pre-nerf the rank 0 skill so that it is not overpowered at rank 2. After all, you can hit rank 2 in less than a week, and you never go down. But the same is in effect when the upgrade is at rank 7 or 11. I have been told, but not confirmed, that when Reavers got their high-rank critical upgrades, their low-rank critical ability was downgraded. Maybe they come out ahead, but consider:
Assume that you get 500 infamy per night. Some people do far better, but some people play a lot or are very good. I would be happy with 500. (Freeps tend to do far better, for the first paragraph’s reasons. If you always win with equal numbers, you tend to get a lot of kills.) That puts you at rank 1 at the end of your first night and rank 3 at the end of your first week. You hit rank 5 a month after that. Rank 7, when my Blackarrow gets the “heartseeker” shot that every level 50 Hunter has, comes at 94,500 infamy, more than 6 months of doing this every night. This is also when Reavers get that critical upgrade I mentioned, but they have a second one (to finish it out) at 11. That is 4.6 years at 500 infamy a night. Based on the infamy-rank pattern, I estimate that puts rank 15 (final) past the two decade point.
One Stalker has been hardcore enough to hit rank 10 in a year. Several freeps are also there (nom nom nom on those newb creeps!). It is probably a mistake to balance creeps around the assumption that they will all be high rank someday. A few will play the game long enough to be really high rank, and I think we are okay with having a few really powerful monsters running around. Considering spider nerfs in Book 13, there is obviously no problem with gutting them further down the line.
(Estimated time to level 50, past your first character: one month. The (f-ing constant) goldspammers in Bree advertise level 50 in 10 days.)