Firstly Lexus RX 350 may be smaller than CX-9 but its considerably larger and much more spacious inside than CX-5:
L/W/H (inch): CX-9 199.4/77.5/69.0; RX 192.5/74.6/67.7; CX-5 179.1/72.5/66.1
Wheelbase (inch): CX-9 115.3; RX 109.8; CX-5 106.2
Who cares about exterior dimensions? Let's look at the interior dimensions.
Lexus RX 350
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Passenger Capacity : 5
Passenger Volume : ft 121.3
Front Head Room : in 39.4
Front Leg Room : in 44.1
Front Shoulder Room : in 57.8
Front Hip Room : in 56.6
Second Head Room : in 39.1
Second Leg Room : in 38
Second Shoulder Room : in 57.6
Second Hip Room : in 56.1
Cargo Volume to Seat 1 : ft 56.3
Cargo Volume to Seat 2 : ft 18.4
Mazda CX-5
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Passenger Capacity : 5
Passenger Volume : ft 103.6
Front Head Room : in 39.3
Front Leg Room : in 41
Front Shoulder Room : in 57.1
Front Hip Room : in 55.2
Second Head Room : in 39
Second Leg Room : in 39.6
Second Shoulder Room : in 54.8
Second Hip Room : in 55.3
Cargo Volume to Seat 1 : ft 59.6
Cargo Volume to Seat 2 : ft 30.9
The RX 350 is 1.4" wider in the front seat and has 3.1" more front seat legroom.
The RX 350 is 0.8" wider in the rear seat, but the CX-5 has 1.6" more rear seat legroom.
The CX-5 has 70% larger cargo volume with the rear seats up, and a little more cargo volume with the seats down.
So the RX 350 is bigger in the front row, it's a bit of a toss-up in the rear, and the CX-5 has a lot more cargo space.
In terms of interior dimensions, the RX 350 is in the CX-5's class. CX-9 is bigger everywhere and has three rows of seating.
My friends 2017 RX 350 is only $5K more than a CX-9 Signature, but it has many features not found in CX-9.
Id much rather to have a 295hp naturally aspirated 3.5L V6 using regular gas instead of 227/250hp turbo 2.5L I4 pulling a 4,000+ pound vehicle!
To me Lexus RX definitely not drives like a boat. The quality-feel interior, although its made in Canada, is a step better than Japanese made CX-9.
With ventilated front seats、panorama glass roof, and many other features in RX, we simply cant find them in any Mazda vehicles.
Lexus Enform Remote mobile app helps you lock and unlock doors, start the engine, resume climate settings, find your vehicle in a parking lot and monitor guest drivers. On CX-9 it cant even offer a regular remote engine start on factory key fob. The Mazda genuine accessory? With a telescopic antenna on a separate key fob?
Seen many complains on our CX-5 weak charging front 1A USB data ports? Theres the same issue on CX-9. Well, in RX it offers wireless charging pad!
Lastly, Id like to present interior color selection between the two, and I digress.
Go the Lexus site and build a Lexus RX 350. If you build one with interior materials and features equivalent to what you get in the CX-9 GT, it's around $53k. If you build one with luxury interior trim, pano sunroof, 360 camera, ML sound, rear seat entertainment, etc. it's $60k. My local Lexus dealer doesn't have a single RX 350 under $50k. They have a bunch of modestly optioned RX's around $53-54k, and a bunch of luxury-trim F Sports at $60k. CX-9 Signature is $45k.
Like I said earlier, if you go for the luxury trim and all the bells & whistles, it's quite a bit nicer inside than a CX-9. But it's still a CX-5 sized car that sells for ~$10k more than a CX-9, so you ought to expect it will be a lot nicer.
Regarding the V-6 vs. turbo I-4, I don't agree with you there either. My wife and I shopped all the CX-9's competitors and drove most of them, including the Highlander with the 8-speed. They all had V-6s in the roughly 290hp range but they were all gutless at cruising RPM. In contrast, the 2.5T n the CX-9 has huge torque at cruising RPM. The V-6s pull ahead above 5000 RPM, but the only time you'll find yourself about 5000 rpm in one of those cars if you're flooring it. The extra power gets the RX 350 to 60 mph 0.1s faster than the CX-9, and the Highlander is 0.2s faster than the CX-9, which is inconsequential. The Honda Pilot and GMC Acadia do better, low to mid 6s I think, but all the power is at the top.
The CX-9 feels a lot stronger and more responsive when you drive it. If you want a little acceleration, you press the throttle a little bit and it instantly accelerates. If you want moderate acceleration, just press a little more. The response is very linear and easy to modulate. It doesn't need to downshift unless you're trying to accelerate moderately hard, and even then it usually just takes a single downshift to get into the meaty range of the powerband and doesn't feel like it's fighting you to stay in too high a gear. In contrast, the 8-speed transmission in the Toyota and Lexus, and the 9-speed in the Honda, Jeep, and Dodge are tuned to upshift early and resist downshifting. When you combine that with an engine with no low-end torque it makes for an unresponsive driving experience. When test driving them, I felt like they wanted to be either in loaf mode or drag mode, and not in between.