When the internet provider drops off your service, they hand you one combined box — modem, router, and Wi-Fi access point fused into a single piece of plastic that lives in the closet near the demarc. For a home with three people, that's plenty. For any business with a handful of employees, it isn't, and it never has been, no matter how many times the salesperson tells you it'll be "fine for an office your size."
The problem isn't the device's raw speed. It's that one box can't simultaneously be a good modem, a good router, a good firewall, and a good Wi-Fi access point. The radios in those combo boxes are designed for a 1,200-square-foot apartment, not an office where walls and metal furniture eat signal. The firewall has consumer defaults. The DHCP table is small enough that printers start dropping off the network at 25 active devices. And when something goes wrong, your only escalation path is the same call center your neighbors are using.
A real small business network has the modem from the ISP in bridge mode (so it just passes traffic), a separate router/firewall behind it (Ubiquiti, MikroTik, Fortinet, etc.), and dedicated access points for Wi-Fi placed where the people actually are. The total cost is between $400 and $2,000 depending on size, not the $10,000 your gut might suggest, and the difference in experience is immediate: faster file transfers, more reliable video calls, fewer "the internet is slow" Slack messages, and a Wi-Fi signal that doesn't drop when you walk into the conference room.
You don't have to overhaul the whole thing on day one. The single highest-leverage move is the Wi-Fi — replacing the ISP's combo-box radio with one or two business-grade access points, even if you leave the rest as-is. The improvement in day-to-day work quality is large enough that most teams notice within the first week. Everything else — the proper firewall, the VLAN segmentation, the redundant uplink — can come in a planned phase two.