Music Composing

First off, there is a big difference between composing a musical piece and producing music.
Since MuseScore is a notation program, a laptop should handle any musical ideas you care to write down. If, however, you desire a 'live-sounding' playback as an end in itself, you won't get it over laptop speakers. Also, you will need something beyond the standard soundfonts supplied with MuseScore. See:
https://musescore.org/en/handbook/soundfont

Also...
Here's a post from a MuseScorer who happens to be both composer and producer:
https://musescore.org/en/node/90671
and, for a video score produced with MuseScore:
https://www.youtube.com/watch?v=Ojqk3EhlWv4

I urge you to read through some of Mr. Schaffter's other forum posts, to learn of his struggle to enhance MuseScore's playback capabilities:
https://musescore.org/en/user/47588
especially:
https://musescore.org/en/node/123946

So...
Basically, MuseScore can notate scores - e.g. from a solo lead sheet all the way up to a full symphony; but if you absolutely need realistic playback as a feedback mechanism to help you compose, then you'll need to go outside of MuseScore's default playback abilities.
That's where DAWs and recording studio software can come in handy - i.e. to produce a polished 'recording' of the musical piece (outside of MuseScore).

Regards.

MuseScore lets you put notes on a virtual piece of music-paper and then to play it back to hear how it (might) sound.   The primary target for its work-product is a human player who will read your score and play it.

You can accomplish a lot of what the person with his workstation-keyboard is doing by attaching a MIDI keyboard to your computer and using it to enter notes ... into MuseScore, and/or into a DAW.   (I snapped up a lovely 88-key controller in the used-equipment bin at a local music store.   It has almost no features or geegaws, but it has ... eighty-eight expressive keys.)

The “very large mixing panels” you see are used for audio production.   A DAW program – I use Logic Pro X – can effectively replicate these features.

I normally write music in MuseScore, then move it to Logic to produce a final version that is mixed the way I want it to.   But I have also created music entirely in MuseScore and it really does sound good.   The software synthesizer that MuseScore uses is no slouch.

Although Logic Pro also has a “score view,” its focus is on audio.   Similarly, MuseScore’s focus is on notation.   Each product excels at what it is engineered to do best, and is comparatively not-so good at the rest of it.   But, I think that this is a very understandable compromise in both cases.   MuseScore can notate anything, even if it can’t meaningfully “play it back.”   Logic can turn out a lead-sheet in nothing flat, but it can’t do all the notation that MuseScore does.

MuseScore allows notes to be entered by pressing keys on a MIDI keyboard, but this is simply “another way to enter notes one at a time.”

MuseScore makes no attempt to let you “play something and expect MuseScore to figure out what you are doing.”   It is notation software, not performance-capture software.   The documentation has this to say:

The MIDI keyboard enters one note or chord at a time.   This mode of note input (often called “step-time entry”) is fast and reliable.   Some notation software tries to interpret “real-time entry,” in which the musician plays a passage and the software tries to produce notation.   However, such results are generally unreliable.   MuseScore focuses on more reliable forms of note input.

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(I’m afraid that I have no idea what you’re talking about when you say, “upload the notes online.”)

Yes, computer entry can be relatively fast. Not so much in MuseScore but many others. Encore is fairly fast—if you have two working hands and I do not. I did for the first 23 years that I've been using computerized notation but I lost the use of my left arm 8 years ago. When I say that I do this one-handed, I am not kidding.

I have more than a little experience here. You always miss the part where I have been doing this for decades. Deluxe Music Construction Set on my Mac+ was crude but was a lot faster and easier than MuseScore.

So MuseScore doesn't have real time note entry. That's ok—it's free and worth every penny. Your constant line that the lack of this important feature is somehow a good thing is ridiculous and you look foolish every time you say so.

That, combined with the lack of a rests palette makes MuseScore too slow and cumbersome for me. Nothing you say is ever going to change that. All professional notation software has those features. That's ok. I have licenses for many of those programs. A few I use.

That MuseScore is free means nothing to me. I would it to be better which is why I revisit it now and then to see. I'd like to recommend it to students but I can't until it's better.

As for lack of a separate rests palette, spend a day in my world. Do all your note entry with only your right hand. Now imagine how much faster it would be if you could just click on a rest instead of having to change the notes palette first.