Here i come choo choo train of explanation:
1. SP is very good balanced to Exp. Bcoz u should die way more often than u do now, propably bcoz u re just playing PvE not PvP like this game is meant to be. Thats why u feel lack of SP.
Good example, here exp loss on siege pvp is turned off, if it would be on, and players that participate in siege would have 10x more SP on lvl than need. Bcoz on each siege u would lose 30-40%, and u dont lose SP.
2. Luck. U drop SB on 1st mob or u drop it in a half year. This is for example CLASSICNESS OF CLASSIC where u have to spend time on farming books instead of just pushing lvls.
3. Almost every stun has base landrate 90% if u dont have stun resist, go for EE, or cry. Why mages got stun so hard? Bcoz they nuke so fast so hard with +12 WIT = balance. U can kill me in second, i can stun u like i want.
4. This how it works on official if im not wrong, ppl use to bug mobs/hide RBs. Following ur idea making 5min respawn comes to same thing like hiding them, coz the problem is not that they re hard to kill, but they spawn so fast. And ppl will always find possibility to bug this.
About this i may be not 100% right. Just like 98% right.