When you ask someone to help in real life, Allah creates actions for them to help you.
When we ask, wali to help whilst he's in grave, Allah also creates actions for them to help, even if you are asking him something "above the means", so for example you are drowning, and you say ya wali Madad, you have belief that through Karama, which Allāh will create, wali can help you.
In both cases, Allāh is creating the actions and the help.
We never attribute divine abilities to other than Allāh, yet we can still say awliya have qudra to do things.
We say, we have qudra in the majazi sense all the time right now. E.g. I have power to pick you up. Yet we know true haqiqi qudra is from Allāh.
Similarly, the awliya when in grave, can have that qudra to give you things, yet it's still metaphorical in the sense that true haqiqi qudrah is from Allāh.
Yes, so we do believe they can help us in actual reality, but there's no difference with us asking them for help whilst they are alive, since in both scenarios we believe Allāh creates the actions and help.
The mushrikīn worshiped their false gods besides Allāh and did share divinity to their gods alongside Allāh whilst still believing in Allāh. They literally took partners besides Allāh and worshiped them even if they did believe Allāh gave them some of divine abilities.
The following is a short excerpt on the subject of tawassul and istigatha from Chapter 3 of Qadi Yusuf Al-Nabhani’s شواهد الحق في الاستغاثة بسيد الخلق
Al-Shaykh al-Ramli said: And the Messengers, Prophets and the Awliya have [the ability to] assist after their death because the miracles of the Prophets and Karamat of the Awliya are not severed following their death.
As for the Prophets, then they are alive in their graves praying and performing Hajj as it has come in the reports. So assistance from them will be a miracle from them. And the martyrs as well, they are also alive, and have been seen, openly fighting the disbelievers.
As for the saints then it is a Karamah from them. [End of quote from al-Ramli]