1- IMHO it is always better to have a real person running a toon. That being said, there are some groups that prefer to keep the loot distribution tight.
2- It is kind of difficult to "break" into an established raid group regardless, until you have proven yourself competent in PUGs. The PUGs may assume that someone in the PUG can supply a support alt, but, they should be more than happy to get a real player instead of trying to run two toons in a PUG.
3- In the end, what a raid group wants is competent players; be that competent player and you will get invites whether you are tank, healer, DPS, or support.
1- That isnt the case at all, I run consistently with nearly every endgame running guild there currently is and can honestly say there is almost never a problem of loot distribution, being either adding more people to run, or between the people in the run already. The main reason Wl/M is preferred as an alt to SOME guilds, is simply due to it being more reliable. You hit a macro and it will do the same thing every single time, no human errors, and less people in group also generally creates a fsater run as IRL occurrences where 1 person has to afk so 11 people have to wait, then 2 minutes later its someone else needing to afk ect... It's more about efficiency then loot.
2- Pug generally try to get as close to 12 real people as possible as its a bunch of random players together, and not the people you're use to running with and their alts you're use to running with. So agreed with this, find a guild that can help you along, and join in when you can or on pugs to show how capable you are at your class.
3- +100