In some occurrences, the Dark Side may seem more powerful than the light side, and it occasionally is.
But you have a strong bias favoring the dark side.
First point is the rule of two. The apprentice has to be stronger than his master. I don't think many masters died of old age.
Apprentices must have a huge attrition rate, between the death in training and the deaths when you try to overpower your master.
So on average Sith are far stronger than Jedi, because the weak and the stupid had died before they can fight any Jedi.
More over, Jedi do not only select the most powerful beings.
Second point, Jedi receive far less training or at least far less specific training. They are the space police. They do not focus 100% of their time to the objective of destroying their opponents.
Third point, the Jedi do not need to do any show of force in order to dominate the Galaxy. Sith rules through fear. So they have to appear almighty. Otherwise they are dead meat.
The Jedi have shown incredible capabilities. Yoda was able to block force moves from some of the most powerful force users you ever got to see.
In legends, Luke and Leia killed Palpatine using his own force tempest.
Luke and Vader apprentice did crash Star destroyers on planets.
Luke's apprentices sent flying away a fucking star destroyer fleet.
The Jedi were proven to be able to cut someone from the Force, and to wipe people memories.
Ok, we did not see the Jedi curing a whole planet, or some impressive feats like that.
Curing a people is incredibly more complex than absorbing his life. And as everyone different, curing a bunch of people may prove impossible unless you are the Force itself.
It may require you to inject some energy instead of taking it.
In the Palpatine/Yoda duel, you can still see than Sidious fears Yoda, even while he is probably the most powerful Sith Lord ever.
So this proves than Jedi are totally able to fight Sith as equals.
Jedi are mainly using defensive abilities, so a Jedi equally experienced and powerful than a Sith would likely nullify his opponents power.
And the victory would be gained by a lightsaber battle.
Sith Lords may have been really powerful and doing incredible things. Do not forget one simple truth, they have always been defeated at one point.
Actually, light Side is stronger, because the Dark Side feed upon itself. It consume his users, breaking their dominion.
Moreover, if you want to dominate the Galaxy you have to dominate or be allied with all the force users. They are stronger than the force users.
Common people are natural allies to the light Side. So the values coming with the light Side are indeed powerful enough to defeat the Dark Side.
Moreover, even if the Jedi were to disappear, the fight for their values and freedom would continue.
Whereas no one would fight for dead Sith. Therefore, the Light Side might be temporarily suppressed, but it will never be defeated and it will dominate the Galaxy most of the time.
Actually in legends it seems that Luke was able to create small black holes and holograms. I don't know the original source but I found this SE link