This is because 99% of teams users use those apps and options every single day. You can right click and favorite items in teams sidebars.

Tasks, todo, planner are independent because they’re different ways to handle those items, allows you to pick the one you want most. Also I believe they all are integrated with Outlook.

Also don’t forget if there’s anything you want custom or anything special you can use Flow to automate the entire system including anything external.

Your complaints kinda solidify the reason most people use and want teams. They provide multiple solutions to address the same problem so you and your team can determine the best option and workflow.

I also don’t think you need to customize it or keep it maintained, but you need someone trained in how-to use it to set it up and then explain to the team how they should use it to make things effective. It’s like having a car and a map so you can go anywhere and get there hundreds of ways and need someone with gps navigation to optimize your route for you.