My take on this issue is a bit different.
It is definitely shirk, if someone thinks that anyone but Allah can solve any problem. As a muslim it is our imaan that all situations in our lives are created by the will of Allah, and therefore, it is Allah alone who can help us. Allah can use any means to help us. E.g. if you have a tough homework and you expect your roommate is the only one who can help you. As a muslim you must believe that Allah will solve the problem, and the roommate will be a source (waseela) to solve that problem. Meaning Allah will make it happen so that the roommate will help you in your problem.
Pious people, those who are true momineen, and those who are greater in taqwa are closer to Allah, as they are superior. Additionally, many people believe that prayers of those who are closer to Allah will have greater chance of acceptance than ordinary muslims. There is great difference of opinion amongst the muslim scholars on this point.
Some scholars, especially those of the wahabi madhab, strongly dispute this and say that every muslim should have a direct link with Allah.... and if there is any problem, the muslim should ask Allah directly. In Quran, Allah Ta'alla has asked muslims to direct all prayers to Allah alone, as He will listen to our prayers and He alone will solve all our problems and grant us our wishes.
On the other hand, there are scholars, both sunni and shia, who say that Allah alone will solve all our problems. And surely Allah listens to all humans and all muslims. However, if a pious person or a mutaqi prays before Allah, because Allah likes the mutaqi person more, He will accept the prayers more favorably. So infact a muslim is encouraged to pray to Allah, in addition the muslim can also request a pious person to pray for him so that Allah bestows more favors on us.
Another important point to understand is that we all know that Quran states that those who die in Allah's name (shaheed), don't call them dead, they are alive, only we (the humans) do not have the capability (to see them). This means that those who are dear to Allah will always be alive (even after their worldly life is over). Only we don't have the inner eye to see them.
By the same token, our Prophet (PBUH), the pious sahaba (RA), Imams (RA) can all be alive, only we are incapable of seeing them. This means, to some scholars, that we can request these pious people to pray for us so that Allah showers more of His mercies on us.
As mentioned earlier, this a point of great different of opinion amongst muslim scholars. In recent times, with an extra ordinary presence of wahabi madrassas and scholars, a growing number of muslims tend to associate all such behaviour as shirk and bid'at.
Only Allah knows the truth. It is best if such issues are not blown up and especially no muslim should call another muslim as 'kaafir'. Everyone has a right to their own beliefs so no arguments should be drawn out to outwit the other muslim. This is entirely a matter of belief. Ofcourse, if we feel that the other person is blantantly carrying out shirk, then it is our responsibility to point out, and if the other person persists, then we should pray for them, and carry on with our lives. Unnecessary infighting only weakens the Ummah and favors our foes, the non-believers.
Adios!