That is only one case, that desn`t contradict the fact that you can benefit (from (having very high Prestige, longer colonial range, extra clolnial grow, extra infamy reduction, extra fort defence, extra diploskill, extra convert chance, and all the juzz that advisers can provide you,) in case you pick NB instead of other idea, and hired another advisor instead of MoM.
It is just one instance where you do not.
Yes, but changing out an advisor is a lot less of a hassle than changing an NI when you no longer need it. By mid-game, if not sooner, I have no need for MoM or NB. Firing the MoM has no cost, swapping the NI costs 3 stab hits which for some nations can be a 2+ years of full investment cost with the unhappy alternative of keeping an NI with zero benefit and the occasional 200 ducat downside. It's likely there are very few situations where any advisor is worth that expense, I personally can't think of any. It is almost certain that the likelyhood of there being 3 advisors that are worth that cost and available is negligible.