I think the biggest elephants in the room are:
1. Reverb (Stock is ok but it definitely can be alot better)
2. Chorus (This definitely needs to be improved).
3. Autotune/Melodyne light style effect, that could also double as a Pitch drop effect by automating the pitch knob with the envelopes
4. Some type of easier to use Glitch type effect like FL Studio Gross Beat. Beat Repeat is nice but Gross Beat is alot more modern with a cleaner/slicker GUI. Maybe Beat Repeat could get overhauled a good bit with the expanding Window like Wavetable to show more details.
That said Ableton's native effects are overall pretty good IMO.
Compressor, Glue, EQ8, Channel EQ, Echo, Saturator, Pedal, Autofilter are some of my favorite plug-ins native or not. It took me a while to really like the Compressor but once I started tweaking the knobs, it is a really nice/clean sounding Compressor thats not too hard to dial-in. Definitely not a character comp but probably on of my favorite "clean" sounding Compressors. Great for vocals, drums, and about anything when used properly.
I hate to say it but when using other DAWs, I honestly feel crippled without those Native Ableton effects sometimes
