Different people will have different setups, depending on their use cases and their personal preferences. 
Personally, I was a network engineer before I ever started using SmartThings for my own use. I have no fear of multiple hubs/bridges as long as each is serving its purpose and has an MFOP (maintenance free operating period) of at least 6 months. This has historically not been a problem at our house except for SmartThings, which does tend to require more hands on maintenance than the other systems we use.
We are 3 adult housemates living in an 1800 square foot house, so pretty typical in terms of household size. However, I myself am quadriparetic (use a wheelchair and have limited hand function), so we do have a couple of systems that most people probably wouldn’t have, like a medical monitoring system.
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So here’s what we’ve got:
SmartThings Station, mostly so we can use Matter with SmartThings
Lutron SmartBridge
2 Philips Hue Bridges
Two separate camera base stations (different brands, but both work with Alexa and Apple Home)
SwitchBot Hub 2
SwitchBot Mini Hub
Solar Energy system base station
Third Reality Mini hub
Flic hub LR
Logitech Harmony Hub (discontinued model, but we have it set up in the family room where it’s controlling several devices, including some battery operated candles)
Old iPhone used as an iBeacon receiving station
4 aqara hubs of different types, including 2 camera hubs. All work as Matter bridges. (I want to eventually get the Aqara M3, which will tie all of these into one network, but I’m waiting for a sale.)
Level lock connect WiFi bridge
Another brand of lock WiFi bridge
2 echo devices with Zigbee hubs inside (this gives us a few Zigbee devices which then have local voice control, our Plan B for if the Internet is out since I am largely dependent on voice control)
Multiple Apple HomePod minis which are also thread border routers
Ring Lighting hub
BroadLink hub (used for an automatic door opener system, which doesn’t work with anything else)
Bhyve sprinkler system
Kumo cloud stations (used for voice control of Mitsubishi hvac system)
Standalone security system with zwave add ons
Standalone Smoke Detector system (we use acoustic detectors to bring The alerts into other systems)
Standalone medical monitoring system
So that’s about 3 dozen, not counting smart televisions and streaming boxes, which technically have some bridge functions.
Plus we have several smart appliances with their own WiFi connections that all have voice control, including microwave, kitchen faucet, washing machine, robot vacuum, air purifiers, etc.
Everything works with Alexa, Apple Home, or preferably both.
I have friends who run very different setups. Some are 100% zwave. Some try to bring everything into home assistant, although sometimes other bridges are required, depending on the devices they select. Some use only Tuya. I have two friends in Europe using only Homey, which has more radios than anything else widely available, but the North American version doesn’t have 433 mhz support, so I haven’t really looked into it.
So as always, different things will work for different people. I don’t think any number is too much or too little as long as it’s working well for you. 
