The thing that makes 10/8 different from 5/4 is that the 10/8 is 3+3+2+2/8. In the same way 8/8 can be very different if the rhythms are accentueted as 4/4 or as 3+3+2/8. But still you can totally "hear" the pulse as 5/4 when listening to 10/8.
Also the funny thing with the 7/8 | 9/8 bar pair is that it adds up as 16/16 so it can be stacked on top of a 4/4 beat.
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Thanks for the explanation! I know there is a lot of fuzz going around for the difference between e.g. 7/4 and 7/8 and whether there is a difference at all, but I get what you mean here. Although, I do wonder... if a part feels like 8/8 | 8/8, such as your 7/8 | 9/8 part, I doubt anyone will recognize it as a weird time signature - I just consider it an interesting division of a 8/8 time signature. Or, in other words, I would classify it as a 16/8 time signature, with a 7+9 rhythm. This is similar to how a 7/8 time signature can have a rhythm of 3+4; I would still say it is a 7/8 time signature, not an alternating 3/8 with 4/8! Or do you disagree?
The way we internalise a beat have a lot to do with the context of the music. Honestly its very rare that I hear 7/8 as a seven time bar (only if the pulse is slow, or if the harmony change every 7 beat or if a melodic cell that fill the bar entirely repeat for several bars). So actually I alomost always hear 7/8 as 3+2+2/8 or 2+3+2/8 ect... depending on the setting.