As he misleads many people, does it mean that Satan is very powerful?

Satans are a species of spiritual creatures that have no capacity for good and that perpetrate only evil. The chief of satans, Iblis was created from Nar-i Samum, that is, from smokeless, scorching fire (Hijr Surah, 27). The original name of the Devil was Azazil. After abstaining from prostrating before Adam, peace be upon him, and after rebelling against this command of God out of arrogance, he took the names Iblis and Satan.

All the efforts and works of satans are aimed at misleading people out of faith, causing them to sin and to indulge in unbelief. The greatest obstacle to the spiritual development of humanity, to their fulfilling the duty of being a servant to God is Satan. In the Glorious Quran, Satan is described as aduww-u mubin (an open enemy). Believers must always seek refuge in God from his evils.

Similarly, in many verses in the Glorious Quran, God Almighty invites believers to seek refuge in God from Satan. Actually, Satan does not possess power on his own. And his devices of apprehension and trickery are weak, too. However, as the works he does are of the kind of destruction and harm, he attains great results with small tricks and devices and thus causes great damage. Therefore, he is seen as powerful and is even accepted as a deity by the adherents of some heretic sects and beliefs. In fact, how difficult it is to construct a building; and how easy it is to demolish it. For a human being to live, a great many of conditions must coexist. However, even though all the other conditions exist, this person faces death because of cutting off a part of body or of not inhaling for a few minutes. All the works that Satan does or the ones he makes them done are of the kind of damage as in the example. Therefore, although his power and tricks are actually rather weak, as he causes great harm and damage, Muslims always seek refuge in God from the evils of Satan.

As the carnal soul, such feelings as lust and anger of humans are also receptive to every trick and evil advice of Satan; sometimes a small trick or device of his quickly sways man and casts him into great spiritual disasters and harms.

This is why the evils of Satan are made seen great to believers and why they are repeatedly admonished so as not to get deceived. Otherwise, satans do not have any power in universe in terms of creation and work and they do not have any interference in the property of God.

WAR BETWEEN ANGEL AND SATAN ON HEART

Angels stir the superior feelings in humans and inspires in them goodness. On the other hand, satans incite inferior feelings in humans and thus leads them to perpetrate evils incessantly.
In a Hadiths by Prophet Muhammad, peace and blessings be onto him, this point is emphasized this way:

Pressure and inspiration comes to the human hearth from two sources. One is from the angel; he says the good and confirms the truth. Whoever finds this in his heart let him know that this is from God; and let him thank God Almighty. The other inspiration comes from Satan; he incites evils, rejects the truth, and prevents human from the good. Whoever finds this in his heart let him seek refuge in God from the evils of Satan. (Ibn Mas'ud)

Whoever wants to spiritually rise and develop must silence the inferior and evil desires Satan inspires in him and must fight against him.