I do not think, any health points have to be increased for a longer mission. As FT you have more than enough medikits, syrettes and self-revive kits - if you choose them.
On a longer mission, the predator would have better chances to attrit the FT step by step - until they do not have any medikit or alike anymore. And even arrow might run into problems, if he is out of medical supplies - against strong predators, right?
The FT then would have to better organize the supplies. This might lead to a match, with different stages. Or, if you wish, to something alike a nerfing the FT with time…
From my POV it does not make any sense to talk about nerfing the firepower on the one hand and buffing the health on the other hand - at the same time. Either you want to improve the chances of the predator - or not:)
In a mission, which just is longer, predators which play less aggressive and more cautious would also have a chance to take down the FT; those predators might not need more health points - as they are more careful with their health.
Longer missions just enables other strategies / tactics. Which would be very nice, if you ask me. And less skilled predator players would have a better chance too - due to time on the one hand and due to less medical supplies in the end on the other hand. The fight at the beginning might favor the FT, the fight at the end then might favor the predator - which is a quite interesting asymmetry:)
I would like, if both cases would be implemented: missions, where you have to stay longer at one point as well as missions, where you have to go to another additional location.
Missions, where you stay longer at one location is more interesting for sniper style on the FT side as well as sneaking around style on the side of the predator. If you have a look at pubs/randoms, both styles do not really exist at the moment. They are not successful here.
Same reason: to diversify the strategies/tactics usable/successful. All that rushing at the moment is fine - but it is just one type of game yet… And this might be getting boring after a while…