A sound argument against necessary tensism

Necessary tensism is the thesis that necessarily tensism is true.

1. Tensism holds if and only if everything that exists in some way, either existed, or exists presently, or will exist. (Definition)

I think a lot of presentists are tensists. The "exists in some way" is a tricky thing. Maybe it should be glossed as: "can be quantified over"?

Here is an argument that tensism is not a necessary truth. In all of the premises, "the present" and tensed expressions must be taken to narrow temporal scope. I take definitions to be necessary truths. I will use "exists*" as an abbreviation for "existed, exists presently or will exist".

2. Two times are temporally related if and only if they are simultaneous or one is earlier than the other. (Definition)
3. Necessarily, if x existed, then it existed at a time earlier than the present. (Premise)
4. Necessarily, if x will exist, then it will exist at a time later than the present. (Premise)
5. Necessarily, if x exists presently, then it exists at a time simultaneous with the present. (Premise)
6. Necessarily, if x exists*, then x exists in some way. (Premise)
7. It is possible for there to exist in some way an entity at a time not temporally related to the present. (Premise)
8. Necessarily, if tensism holds and x exists in some way, then x exists in some way at a time temporally related to the present. (By (1)-(6))
9. Possibly, tensism is false. (By (7) and (8))

No tensist will be convinced, I suppose, since they will deny (7) (they may quibble about other premises, but I don't think these are a big deal). But I think (7) is very plausible. Surely it is possible for there to be parallel time lines with no temporal relations between them. Likewise, surely it is possible that there be no fact of the matter to the effect that a short-lived entity on Alpha Centauri has existed pastly, and no fact of the matter that it exists presently, and no fact of the matter that it will exist futurely. (One just thinks a little about relativity theory, and this becomes plausible.)

Moreover, not only is it possible that tensism is false, but we are not in a position to know tensism to be true. For we are in no position to know that there are no parallel timelines, and if there are, then tensism is false.