Well, it sort of depends on what you do, and, where you are.
For State/National parks, there is often not a lot of choice in camping spots. Low-lying areas are usually prevalent where people and cars have compressed the soils. In a heavy rainstorm, the site is often one big puddle. In this case I use an Exped Sirius. It has a 10,000mm bathtub style floor. It has been through 5 days of continuous rain, but never leaked. It was sitting in a 2" deep site-wide puddle and didn't leak. Would I take it backpacking? No. It weighs 5.5pounds. This is for getting to the ADK's and for comming home, often at a state campsite.
I also have a mesh tent and tarp that weigh a little under two pounds (including lines, but no stakes.) Stakes bump the weight up to just over 2 pounds. In spring/fall (when the weather says cooler nights) I often just take the tarp. Backpacking is different because you can select the site you want to set up on. A slight mound, or raised area will keep the grass/duff floor dry, generally. If you anticipate a hurricane, a larger mound works better. (Yes, I have been out in a hurricane and stayed dry at night.) I recommend a small can of bug spray to keep ground insects down. Saturating a bandana with bug spray will last about a week if you keep this in a baggie, taking it out and spreading it under your bag before going to bed. Fleas, chiggers, spiders, etc all can be an anoyance at night and if they get into your bag. Mosquitoes, and the rest are usually covered by permethrin in my cloths, often, these are placed on top of my bag to dry.
Hiking in the rain, at least in the ADK's, is difficult. Slipery roots and rocks can cause all sorts of falls. It alsways slows you down. Usually, by 1000-1100 things have dried up some. Just in time for the afternoon rains at around 1600-1700. Being the first one on the trail means wet pants, then socks, then shoes on a slipery trail. I often wait till 0900 to get going...
The UL polycro or similar (painters drop cloths, tyvec) have a way of becomming punctured easily. I quit using them about 5-6 years ago. My pad works well enough as a ground cover. This year especially, the heavy and frequent rains have left the woods quite wet. Everything is damp, all the time, when I am out. My pack weight often increases for a day or two after I leave, due to this. Water to drink is NO problem this year.
Soo, it really depends on where you are camping. Often a pine tree wiill have a dry area near the root bole. I like to set up there. Sometimes you can find a dryer area in the woods to set up. This often means raking up some duff to fill in low spots for my bed. Downed smaller branches can be used, too. Just cover them with leaves/duff. For the canopy, 1500mm is not enough, sometimes misting right through the fabric. New tarps will often get a coating of 20-30/1 mineral spirits/caulk. I believe this raises the HH to about 2500-3000mm for a couple ounces in weight.