Yea.... So extended mags are NOT meant to increase how many mags you can hold. It's so that your can hold the trigger for longer.... Like you said. Which, btw, by definition is exactly what it's supposed to do. Your complaining about something doing what it's supposed to do.
Monster Hunter isn't "too easy now". The base games are always easy, made even more so by QoL changes over the previous title. This is true of World, Rise, and Wilds. Vanilla Monster Hunter World had about 3 genuinely challenging monsters. Wasn't until the updates and expansion came out that players were really feeling the difficulty.