it's mostly about the power and the speed
Routers may be rated from 1 to 2 Hp, up to 3 1/2 HP, but that's based on some high power mathematics and assumptions. The router motors are "universal" AC/DC with brushes where the shaper motor are rated a real 3 HP and are induction run only, and require 220 Volts.
That's the power story briefly.
The shaper is meant to turn slower, either 7,000 RPM's or 10,000 RPM's usually just 2 speeds. The router motors turn from 8,000 RPM's to 22,000 RPM's. The smaller 1/4" shank bits need to spin at the 20,000 rpm range. The larger raised panel bit up to 3" in diameter need to spin slower, around 8,000 RPM's or so.
So, you can't really use smaller dia bits in the shaper with great success, but you can use the larger panel raising bits in a router table ....IF you slow the speed down appropriately.
Bottom line, smaller bits in the router table, and large cutters in the shaper for best efficiency. There are many more profiles available in shaper cutters, at considerable expense, than there are in large diameter router bits. A well equipped shop will have both machines, but for just starting out, a good powerful router in a solid table, maybe with a lift, will do a whole lot of profiles.... :yes: