In Krishna's case, each of his major wives had 10 sons. In the case of the 16,100 wives he captured after killing Narakasura, the reason he married them was that they had no future: no other man would marry them b'cos they had already been violated by Narakasura.
Pradhyumna marrying Rukmavat and Anirudha marrying Rochana were unhealthy, given that Vidharbha was already an ally and bound to Dwarka due to Rukmini alone. Same w/ Arjun & Subhadra: Dwarka was already beholden to the Pandavas due to Kunti being Vasudev's sister. Subhadra's marriage to Arjun was to prevent the alliance from being trumped if she married a Pandava enemy, like Dury. Also, as Shalya turned out to prove, being an uncle of the Pandavas didn't prevent him from joining their enemy.
Chitrangada was a genuine romantic interest of Arjun's, and did nothing for the Pandavas politically: Arjun's son Babruvahana was totally out of the Pandava succession, and even though he was king, he didn't participate in the Kurukshetra war, even though his father was there in it. Also, Manipur was nowhere near Indraprastha, and Pragjyotisha - Guwahati - was a Kaurava ally.
Rukmi was an enemy of Krishna even after Rukmini.
It was perhaps idiotic to imagine he would change after Rukmavati, but it did happen.
Agree re: the 16K women.
Chitrangada Arjuna romance is from the imagination of Tagore. There is nothing in the text to suggest there was any romance, at least not from her side.
I did not claim Manipura was near Indraprastha. I said because of its location ie in the north east, it would serve well as buffer against invaders. At that point, Pragjyotisha LATER functioning as Kaurava ally would not have mattered.
Same reasoning for Babruvahana mot being in succession line. When Arjuna married Chitrangada, the succession was several years into the future and would not likely have been a thought.
If you mean that line about being struck by desire at the first sight of her, Arjuna was similarly struck by desire at his first sight of Panchali and Subhadra as well. I guess it helps the ladies in question were not crones. But the one time he was struck by desire (Ulupi) and saw no political benefit, he chose not to acknowledge her as wife until much later in life.
Kunti being Vasudev's sister did not cause the Yadavas to offer help in any way, shape, or form. Nor did she ask for it. In this scenario, Subhadra being married to Suyodhana would have decidedly changed Yadava attitudes. So yes, Arjuna Subhadra was very much political.
The blame for the marriage alliances eventually not counting except in the case of Panchal and Krishna can solidly be laid at Yudhishtira's feet IMO. Who would want to follow an emperor like him?