Are planet aspects usually more stronger than sign placements?

Yes the planets tell the big story and the aspects (how the planets interact with each other) show whether the planet is working 'well' or not working so well.

I think the most important thing to do when looking at a chart is to notice the hard aspects of the conjunction, square, and opposition as these are all Life Lessons that are to be worked on in this lifetime.

The sextiles and trines are karmic rewards for something done especially well in a previous lifetime. These are the "good" aspects that have been 'earned' from good deeds in a prior lifetime.

For example, say you are looking at a chart and you notice that the Sun and Mars are conjunct (very close in degrees). Without even knowing the signs we know that this one is a ''warrior' and has a life lesson in learning to only choose worthy battles to fight. If the person is unaware of this tendency then they won't make much progress in learning to assert ones self when necessary and to avoid getting involved in situations that are not worthy of your time or effort.

So just from that one aspects we know that this person has a nature that tends to 'battle' and in this lifetime they need to work on only choosing worthy battles to fight and avoid unworthy battles.

So that is quite a bit of knowledge for just one aspect. And if desired you can then look at the signs of the conjunction of Sun and Mars and this will give you a better idea of their 'style' of fighting. Sun and Mars in Aries would be especially strong because Mars is the Ruling Planet of Aries. So this is one strong conjunction (life lesson)

Another example. Say one has Moon conjunct Uranus in their chart. This is one difficult aspect because the Moon is our emotions and Uranus is our non-traditional 'rebel so just from knowing this information we know that this person has trouble controlling their emotions because Uranus is known for its unpredictability and when this trait of 'abrupt change' is 'added' to the emotional Moon we can see there are going to be issues regarding consistency in emotions.

To have ones Moon conjunct Uranus is like having spontaneous emotion but not in a 'good' way. Uranus hates 'routine' and so when Uranus is 'bored' that is when the buttons can be 'pushed' in order to get some 'argumentative emotion' to manifest.

This aspect allows the emotions to be thrust into chaos therefore this is another life lesson needing work in this lifetime. Moon conjunct Uranus is a tough aspect needing to be overcome in this lifetime. Again all this information just from two planets in aspect. You just can't 'get' that kind of information from the signs alone.

So great question because it is the planets that have the most 'force' in a chart and the life lessons are most important because when we overcome them we are on our way to evolving to a higher state of being as 'love' is the goal here on earth. Learning how to love others. That is the main goal in life for all of us.

Hope this is helpful and good luck and bless you too.