Is there a one-word adjective for two people (or objects) of the same weight?
I think the two sides of the political spectrum are substantially and inherently different. One can't just see them as two [adjective-in-question] opponents fighting it out.
How about a compound adjective? Say, for two martial artists; Is there an attributive adjective for their weights being equal? (One similar to like-minded maybe.)
The word that has exactly the meaning that is sought here is equiponderous. Its advantage over the words proposed in the other answers is that it specifically means being of the same weight (which is what the OP asked for), rather than just being similar, comparable, matched in some way. Its disadvantages are, first, that it is arguably obsolete, and second that, even if one does not regarded it as obsolete, it is likely to be understood only by a small percentage of English speakers. So, if one wants to use a word that means of the same weight, one should say equiponderous, but if one wants to be certain that one will be understood by average people, one is likely to be better off using one of the other words proposed on this page, which do not have exactly that meaning, but are close enough.
being in a state of balance : having different parts or elements properly or effectively arranged, proportioned, regulated, considered, etc.
- Put together as associates or equals; consisting of equals, or of complementary or corresponding elements. Frequently as the second element in compounds, as well-, ill-matched, etc. (for more established compounds see the first element).
...One can't just see them as two equally matched opponents fighting it out. If two opponents are not "equally matched" one of them will be "outclassed" and most likely defeated.
Commented
Jan 13, 2020 at 21:29
The term equivalent is apropos:
3: corresponding or virtually identical especially in effect or function
Although equivalent has other definitions, the above indication that both sides can't be seen as having the same function seems to make you point.
In a literal sense, commensurate means exactly that:
1: corresponding in size, extent, amount, or degree
2: equal in measure or extent
In my experience, "commensurate" is typically used to describe qualitative properties (e.g. matching a punishment to a crime). It doesn't drop into your sample sentence perfectly, though.
They're on on par with each other, or not.
par - common level
on par with - the same as or equal to someone or something
While not exactly what OP asked for, it could be noted that for matched or mismatched weight/strength opponents in some competitive field, including politics, it is quite common to refer to their skill or status as "weight", as if they were boxers: heavyweight or lightweight. Heavyweight implying substantial achievement in the field.
So, rewriting the original quote, it could be said:
I think the two sides of the political spectrum are substantially and inherently different. One can't just see them as two heavyweights fighting it out.
isobaric
If you're comfortable with a tinge of neologism, I'd suggest 'isobaric'. The Greek root 'baro' means pressure or weight (google 'greek root word baro'). Scientists use the term most commonly to mean contours of equal pressure, for example on weather maps, but this proposed new connotation is a stretch neither in the vernacular nor in its classical roots. After all, the medical term 'bariatric surgery' refers to stomach stapling and other procedures ultimately intended to help control weight.
