1. T-Mobile does have a lot of dead spots in Griffith Park. So do the other carriers, just not in the same places.
2. There are at least 6 cell-sites on LAX, in addition to those around the periphery.
3. See Griffith Park.
4. I think you'll need to be more specific about exactly where in Malibu you're having trouble. Various 3rd-party coverage maps show good service along the beach but some issues in some of the canyons.
5. Again, T-Mobile is going to ask for specific spots, rather than just "downtown".
Do you experience the same dead spots when you are out of your vehicle? Unfortunately, manufacturers removed the external antenna jacks from almost all phones. Having an outside antenna used to make a big difference in reception in a vehicle.
I mean I think the most frustrating besides Griffith Park for me is like West Hollywood and Beverly Hills near the top of the hill, it seem like there is a ton of dead spots on the tops of the hill.
I don't have any specific spots just by tall buildings.
So specifically my issues are mainly Malibu the northern parts (north of the shopping center area) by the ocean and the canyons and also that road after the Palisades Village Shopping center (the one off sunset ) that goes between a canyon 0 reception there and then after that canyon part there is a ton of apartment complexes that I get Uber requests from all the time.
If I run into any specific spots this week next etc I'll remember to come back and share I'm all over LA usually. Sorry had issues remembering specifics since I have driven now for like 2 years I just got frustrated and switched from T-Mobile then switched back so this is a pretty big issue for me.
My suggestion is that you check out the 3rd-party, crowd-sourced coverage maps at Sensorly.com, RootMetrics.com and CellMapper.net. See how your experiences compare with others' experiences. Then call 611 and file a coverage complaint for each individual spot. It's a bit of a PITA because your T-Mobile "team of experts" is going to start from the assumption that you are a clueless dolt who hasn't even turned his phone on and has to be instructed on how to do it. Once you get through to tech support, you need to have a list of addresses or cross streets.
I will mention that it may be difficult for T-Mobile to make improvements in some locations due to zoning difficulties.
I'll also mention that iPhones are generally not regarded as having reception equal to similarly priced Android devices.