This assumes a certain specific definition and idea of God. It also does not account for the ways in which people incorporate their various views and dispositions into an overall approach to dealing with life. If there is confusion, it is not necessarily needless. And contradictions will be an issue even if one accepts the particular point of view that you have articulated here.
Your comment sets up a series of comparisons that I would like to address briefly:
Anatta versus "self-existent": God might be regarded as not-me, not-mine, not-self. The understanding of anatta applies to that which presents itself in one's own experience. It is a pointless exercise to direct an analysis of anatta to some other perceived person or being and argue that he, she, or it does not have a self. From the perspective of practice, a God concept might actually help to cultivate an understanding of the anatta nature of reality. (Or it might not. This is merely to illustrate that there are other ways of looking at this issue.)
Dukkha versus "benevolent": Your argument appears to be that a benevolent God would not permit suffering. The understanding of Dukkha applies to that which presents itself in one's own experience. It is pointless to theorize whether some other agent besides the greed, hatred, and delusion driving one's own kamma contributes to suffering. One the other hand, from the perspective of practice, a God concept might help one to understand metta.
Anicca versus "eternal": God might be regarded as renewing, transformative, creative, or even as the alpha and omega, the life and death, in other words, as everchanging reality. The understanding of anicca applies to that which presents itself in one's own experience. When we do not understand anicca, this might lead to strong preferences for one thing over another, and to clinging. A God concept might help one to see past that and arrive at a better understanding of anicca.
The point is not that these views of God are correct or true or false. Rather, the point is that we do not know how a particular individual might conceptualize God, or internalize God concepts, or whether belief in God might be helpful or unhelpful.
We do know this: It is not Dhamma to disparage other faiths. It is not Dhamma to try to persuade others to come over to your ways of seeing things. If people believe in God, what business is that of ours? The beneficial teachings of Dhamma are as true for those people as for anyone else. There is no benefit in oversimplifying belief in God and making a blanket statement that such belief is always unhelpful, confusing, contradictory, and so on. Saying such things is not Dhamma.
Best wishes.
Perhaps it wasn't clear at first, phrased so succinctly. It may help to elaborate a bit more, step by step.
First consider the Buddha's teachings on the false appearance of immortality that leads sentient beings to fabricate the notion of an eternal God. For instance, in the Brahmanimantanika Sutta (Majjhima Nikaya 49) the Buddha explains how Baka Brahma, immersed in ignorance, falsely imagines himself to be constant, permanent, and eternal. This is complemented by another early discourse, the Brahmajala Sutta (Digha Nikaya 1) in which the Buddha explains how Brahma believes himself to be the first cause - "the Conqueror, the Unconquered, the All-Seeing, the All-Powerful, the Lord, the Maker and Creator, Ruler, Appointer and Orderer, Father of All That Have Been and Shall Be" - based on his long life. Even god-like beings are subject to the three marks (tilakkhaṇa) that characterize all existence - 1.) impermanence/transience (anicca), 2.) imperfection/unsatisfactoriness (dukkha), and 3.) impersonality/essencelessness (anattā
.
Anattā versus "self-existent": Despite the anomaly that occurs in the rare instances when an impersonal God might be regarded as "not-me, not-mine, not-self" (
netam mama, nesohamasmi, na meso atta), it is still contradictory to attribute self-existence (the nature of being Uncaused, Uncreated, Unborn, etc.) of any sort to any such entity. A first cause and underlying substratum is rejected by all forms of Buddhism. (This does not imply that other faiths should be disparaged for believing otherwise. It likewise does not imply that it is necessary to persuade anyone to see things the same way. To suggest so is to set up a massive strawman and does not address the actual content of the discussion. As above, this is merely to illustrate that there are other ways of looking at this issue.)
Dukkha versus "benevolent": It is not that God (if one is assumed to exist) contributes to suffering, but that God allows it to occur, which is contradictory. The Buddha rejects this notion in the Tittha Sutta (Anguttara Nikaya 3.61). Surely, the concept of a God may assist with the cultivation of loving-kindness (mettā-bhāvanā
. When the Buddha spoke with a Brahmin, he spoke in the language of the Brahmin, with terms the Brahmin could understand and relate to. For instance, in the Tevijja Sutta (Digha Nikaya 13) the Buddha describes God as a metaphor for different qualities of the heart. These include loving-kindness, compassion, sympathetic joy, and equanimity. In the Brahmavihara Sutta (Anguttara Nikaya 10.208) the Buddha describes these "abodes of the gods" (brahmavihāras), noting that the gods represent the embodiment of the aforementioned qualities. They are symbolic devices.
Anicca versus "eternal": God, whether personal or impersonal, is by nature defined as a permanent substratum to existence. Despite being a so-called "everchanging" life force in the minds of some, there is nonetheless something about it that pervades all things and neither arises nor passes away. This crosses the line into the mistaken view of eternalism (sassatavada), which again contradicts direct experience.
On and on we go. Sabbe sattā sukhi hontu. May all beings be truly happy.