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All concrete will crack if you don't put in some form of relief to allow the concrete to do its thing. The idea of cutting lines is that when the stress is relieved as it cures it will follow the lines or expansion joints as it does so, He was also supposed to have fiber added to the concrete mix, but he decided that was not necessary and the end results shows what happens when you don't.
You are getting some misleading information. It's true that all concrete cracks, but those cracks should be so tiny that they are impossible to see.
When a new concrete pad cracks, it's because they used too much water in the mix. They do this because it makes it a lot easier to spread. Excess water has to leave the mix when it evaporates. Water takes up space, and when the space taken up in the concrete pad goes away, then that causes the concrete to crack.
A proper slump is when the concrete does not flow, it piles up on itself and remains in place. This requires a massive amount of effort to spread out. Guys that do this every day would rather have an easy day instead of a hard day. They don't care about your job, they are gone and will never return.
Rebar is the only product that actually holds the cracks together in a concrete pad that actually works. Fiber helps, but it does not replace rebar. Welded wire only works if it's in the middle of the pad, and this is impossible on anything that you walk on when spreading. It's great for walkways, but horrible on building pads. Rebar has to be placed on chairs. The biggest lie in concrete is when a lazy contractor tells you that they will pull up the rebar while spreading the concrete, and it will stay in the middle of the pad while they walk on the rebar. Chairs make it harder for them to walk around while spreading the concrete, so they don't like that either.
It's not uncommon for a large pad to have low areas that only show up when it rains. The pad will have shallow wet areas that might be a quarter inch lower then other areas. That's just from the level of skill from the crew spreading the concrete, and the bigger the pad, the more common it is.
Cutting the pad does several things. When concrete gets hot, it expands. When it gets cold, it contracts. Concrete roads have to be done in sections so it can expand and contract throughout the year. Some people believe that their building pads also expand and contract, so they want it cut to allow this to happen. In my opinion, it's not needed if there is a building over the concrete. More commonly, people have their pads cut because they believe their concrete work is questionable, and they hope that when it cracks, the cracks will be hidden by the cut lines. If the pad was poured with the proper slump, rebar was used and set on chairs, cracking will be so minor that you will never see it.
Soil compaction under a pad gets a lot of blame for cracking, but this takes years and years to happen. It's not uncommon for there to be hollow areas under a pad. I see this in houses all the time that I'm remodeling. The concrete is strong enough to bridge these gaps and you never know it's happened. The only times that I've ever seen concrete fail from a lack of soil compaction is at the corners of exterior load bearing walls. And it's very obvious, the concrete has broken off and dropped an inch or more. Random cracks in the middle of a pad are not from the soil not being compacted, they are from too much water in the pour.
From what you have posted, it sounds like your concrete contractor was a hack. He may or he may not know what he is doing, either way, he chose to do a poor job for your project. Some do this intentionally to make a quick buck, others just don't care, and if you watch YouTube, you will see quite a few on there that are just clueless.
