Yes, warframe will lose players in the summer, but not because of Nexon and their game. People play less because its too warm, and they do something else. If the game is good and warframe loses more players over a long period of time, that's the best you can imagine for the game. That means they have to think a little harder about changes and directions the game will take to strive.
I think you have some good points on your list, but some points show that you havent played certain warframes or just going by youtubers opinions. Its okay to have certain metas because DE will nerf them in the long run, even if they dont know why something is popular. they just nerf because its "most played."
Armour-stripping abilities are popular because corrosive projection was nerfed a long time ago. Now you dont have to use shattering impact, nekros terrify, or hildryns pillage. Just use two green shards and a co-primer to your liking, and you can kill the most durable enemies. We have operators who can make us survivable or do massive amounts of damage, overall being faster than warframes without the cost of bullet jump mods and arcanes. Almost every weakness can be avoided or fixed with ingame mechanics.
You have the possibility of finding people who fit your playstyle. Old warframes will see changes because thats what we get over time. Overall, warframe will continue to change, but at their own pace because they dont have a competitor. Lets hope Nexon and other companies will give us good games with new ideas so DE can come up with something new, even tho they already did great this year, there is always room for more.