I know this is how people in the 80s and 90 imagined the future and a lot of concepts were probably too far fetched for them.
BUT... why arent they using drones to explore planets? why are there not more drone-spaceships? why does enterprise need a crew to begin with? Why is there so little automation? Why so few uses of AI in general?
I am saying this as a star trek the next generation person. I'd also expect them to have full video and sensory streams of any surface mission teams.
They also don't have armies in star trek, like, if it makes senses to send 5 armed people why wouldn't it make sense to send platoons or batallions in some cases? it is always individual enemies they never seem to face entire armies on foot.
So, this one is a little more justifiable.
Phasers, and starships. And because ST isn't about war; it's about diplomacy.
With the exception of the Borg, there are no personal shields. One person with a phaser is a WMD; it's a sweep-able, incredibly destructive weapon, and if you're not interested in merely maximum casualties, it also has an effecting area-effect stun mode.
But the other reason is starships. Ignoring plot devices, orbital targetting is incredibly accurate and starship phaser banks can anihilate entire areas. If you tried to move an army across an area, it could be vaporized by a single enemy starship.
Either the enemy has superior technology, in case it doesn't matter if you send 1 or 1,000 people; or they have inferior technology in which case you need only one person. And if you have air (space) superiority, you can level cities with even a smaller starship.
So ST is more like special forces making surgical strikes, sending in problem solvers and diplomats, and hoping nobody starts shooting in earnest.
Because phasers are OP.
I had no idea about this tbh they come of as very tame weapon, especially the whole stun setting part.
It can be used that way, sure, and the Very Civilized Starfleet uses them conservatively. But a beam weapon that is capable of disintegrating anything (unshielded) that it touches is crazy powerful. And those are only the hand phasers; we don't often see the phaser rifles, but holy heck. If phasers scale like projectile weapons do, a single phaser rifle would be capable of vaporizing entire buildings, tanks, aircraft.
Wouldn't a simple mirror be enough to reflect the rays back to the sender?
Phasers aren't lasers, and the beam isn't light; so, probably not.