It's a + 1 to a Stat and 4 proficiencies. More complex, sure. But not complex.
If + 1 to two stats is a 1 on the (1 to 10) complexity scale, I'd put the proficiency feats at a 2 or 3.
What kind of scale? If the currently most complex feat is 10 on the complexity scale, most feats which currently grant proficiency in weapons could be a 9 or 10, since they all add abilities you have to keep memory of. Other proficiency feats such as Loremaster or Alert are less complex because they mostly grant "write (on character sheet) and forget" benefits, but still have 3 different benefits, and sometimes you even have to choose them. This is lesser complexity, but still complexity.
Anyway, my main main point is:
- people who hate feats probably do so for various possible reasons. Maybe the most common are a) fiddly bits i.e. small benefits that aren't significant enough, b) more things to keep track of (i.e. added complexity)
- having the option of learning new things
during the campaign is quite natural for the game, and yet currently there is no
easy way to gain new proficiencies. If you want a new proficiency, you have to take it through a feat or (yikes!) multiclassing. That means A LOT of extra baggage, when all you want is just 1 more skill or 1 more weapon!
- that means people who hate feats, if they ever wish to get 1 more proficiency after level 1, they will have to take a feat, which now has even more fiddly bits and things to track of than in previous editions...
I'm just saying that if feats were same "size" as in previous editions, this would not be a problem. A player could at some point choose a feat OR a +1 to an ability score OR a new proficiency. The player who hates feats would not need to take any unwanted fiddly bit or whatever, but could still get just that extra proficiency she's looking for.