The base amount is reduced because there's now a variety of ways to raise it, you can easily get it far higher than 5 even in the early game now.
Looking at one change and jumping to conclusions makes no sense, 1.5 changes a lot of things. You can't just take one patch note in a vacuum and assume you understand exactly how it's going to play out.
@Wiz Just do the below to appease these Sector naysayers.
Could give sectors worthwhile bonuses. These bonuses might take time to reach its maximum value.
Research Sector +10% Science, +5% Science in adjacent systems
Industrial Sector -10% Ship production time, +5% ship building time in adjacent systems
Trade Sector +10% Energy production, +5% Energy in adjacent systems
Frontier Sector -10% Pop Growth Time bonus and +20% migration attraction
Core Sector - +5% Energy, Mineral and Research production, -5% ethics divergence in adjacent systems
Tourist Sector + 5% Happiness, +1% happiness for every planet with a special attribute to the whole nation
Border Sector minus 20% cost and maintenance of defense installations, +20% sensor range, +20% border excursion. Your border can never shrink.
Iron Fist Sector (Militarist Only) - 10% Faction support, -5% faction support in adjacent sectors
Re-education Sector - 10% Ethics divergence, -5 ethics divergence in adjacent systems
Luxury Sector - Doubles strategic resources minus 20% energy and mineral production (so you can share with your Fwends)
Bastion Sector - Starbases, Defensive installations and armies have +20% hit points
Communications Sector - ethics divergence distance modifier is halved, ethics divergence distant modifier is quartered in adjacent systems
Flashpoint Sector - you consider a certain distance beyond your border to be your space. Any nation that has closed borders to you in this space is considered hostile and you can attack ships and installations at will. You can fly into closed border space up to a certain distance. Generates threat with adjacent neighbors. Allowing you to possibly antagonize another nation into declaring war.
Holy Sector - Spiritualist pops are attracted to this sector and are happier in this sector. Materialists are not and generate disgruntled factions in this sector.