In Syriac, mar (ܡܵܪ mār) doesn't mean "God," it means "lord." There's a related form ܡܵܪܝܵܐ māryā that means "Lord God." The Syriac word for "love" referenced here is actually ܚܘܿܒܵܐ ḥobbā, with a different vowel and a geminate /b/. Marhaba is an Arabic word. https://twitter.com/tefehten/status/1290207994416787457

The origin of marhaba is the Arabic root rḥb, which means "to be wide, spacious." From this came the greeting أَرحَبَت عَلَيكَ وطُلَّت “may (the lands) be spacious for you and moist with dew,” which makes sense if you consider the ubiquity of nomadism among Arabs in the desert.

Marhaba is مَرحَب marḥab, applying the root to a pattern maCCaC that is used for all sorts of nouns of place (اسم مَكان ism makān in Arabic). Marḥab therefore means "wide, spacious place."

This word occurred as part of another greeting: أهلًا وسَهلًا ومَرحَبًا ˀahl-an wa-sahl-an wa-marḥab-an “kinfolk, smooth land, and spacious land”. These words are in the accusative case (-an), indicating they follow an implied verb such as صادَفتَ ṣadafta “you've chanced upon.”

Over time, as the case system deteriorated in Arabic, the final -n of the accusative dropped out, and what resulted are two phrases, ahla wsahla and marḥaba, that have lost their original meanings and become stock greetings that simply mean "welcome" and "hello."

Probably the etymological opacity of marḥaba as well as its adoption by a number of non-Arabic languages makes it particularly susceptible to exotic folk etymologies, but this is a plain old Arabic word (with an interesting story all the same!).