What is to be gained by it other than brand yourself as a jack-ofX?
Each Era the game becomes progressively more difficult. CMap fights are harder and more expensive to negoriare, GE is tougher, tech is more expensive.
The big payoff in this game for the last year+ is GE. The rewards are more frequent then any other aspect of the game and are comparable to or better then the best available from DCs and Events. Significant GE prizes do not scale, they are the same form Era to Era and are essential to accelerate game state advancement. However, the effect of those prizes is magnified in earlier Eras.
The fighting is easier in earlier Era GE, a full set of leveled attack GBs with Traz+Rogues makes GE a cakewalk in early Eras.
The same theory applies to DCs, the next easiest way to get good Prizes. The top DC prizes don't scale/ As is the case wiht GE, why not get those prizes sooner rather then later?
The only good reason to move up in Era is to unlock more Expansion to cram in more GBs and GE and DC prizes.
Did INNO intend this? I don't know, but camping is an inevitable consequence of INNO's additions of RQs + CF, DCs, GE, combned with Events requirong Tech and CMap progress.
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Camping is allowed and is a successful strategy that combines well with other succesful stratefies.
The question becomes what can one do if one does not want to camp?
Play the game the way you want.
About the onlt bad things that campers can do to you is snipe the Rewards on GBs from you and plunder you. Both problems can be mitigated, if you need help with either ask and some one will point you in the right directions.
Good luck!