I like playing ICP from time to time [or all the time in case of current event] but to not lose splinter I go to MM to kill groups of blue/yellow mobs for quick splinter [sometimes first group is drops it] and then go back. Doombots are my favourite enemy group for that purpose, they drop splinters almost every time [after the timer allows them] and they have some nice chance to drop two [not as big as sisters in abandoned subway but nice].
Without this tactic I would have a lot less splinters while playing in ICP only [I play less hightown and there is also less problem with splinters there - but still].
Maybe this is one of the reasons ICP is less popular?
In ICP splinters drop best [most reliably] from rocket-rexes coming out of containers, less so from MGH burtes at wearhouse and Taskmaster's mercenaries. Adding more yellow groups or some enemies with splinter better splinter drop rates would be nice and jumping from patrol to patrol wouldn't be required to get similiar amount.