Emeral - For these being your first three rates, these are pretty good. You seem to have a good understanding of being able to identify problems and fix them which is good. Looking over your first rate, I agree with the changes you have made. I like that you did not make any Pokemon changes to this user's team. Sun Teams are very dependant on synergy and most of the time do not need Pokemon changes unless it is very necessary and there are problems with the teams synergy. A lot of the time, moveset changes are just as significant as Pokemon changes, as one move can completely change what you can hit super effective, and what you can wall successfully. My only suggestion on the first rate would be to suggest 0 Special Defense IVs too. This will make sure even the weakest Special moves will bring Dugtrio down to it's Focus Sash, being able to activate it a lot easier and have the freedom to power off more high powered Reversals. This is very important because the user has a huge reliance on Victini to deal with Special walls, namely Chansey who look annoying for his team otherwise.
As for your second rate, I agreed with the Venusaur change. It gives him arguably a much better Chlorophyll abuser, with much better bulk as well as being able to actually force switches, unlike Jumpluff. One thing that I felt you could have improved was actually explaining Venusaur's EV spread, to inform the OP of what the EVs do so he knows what to outspeed under Chlorophyll and can alternatively change them to his liking. As for your Jellicent suggestion, I agree that it is a good fit over Rotom, providing him with a Spinblocker, however he is still weak to Calm Mind Reuniclus and Stall in general. You mentioned Jellicent being able to beat most common members of Stall teams, but the set you suggested lacks Taunt. Jellicent cannot beat Chansey, Reuniclus or Ferrothorn without Taunt, all of which Taunt helps to shut down. Taunt would be a good option over Scald, as with Will-O-Wisp and Sun halving Scald's power, you don't miss out on anything you would before.
The third rate was one I found myself disagreeing with for a couple reasons. First of all, as an aspiring team rater, you should have picked up what the purpose of the team was.
The basic strategy is to identify and eliminate or cripple certain key threats in order to allow Chandelure, Landorus, or Breloom to sweep.
The OP is basing his team around being able to sweep with either of these, so you will try to do what you can to make this job much easier for him. It is not a good idea to replace any of these Pokemon, as it takes away from the purpose of the team and becomes a different team. Although the changes you suggested arguably make the team better, you deter from the original purpose, and by adding Heatran, Jellicent and Amoonguss, this is no longer an offensive team, but more a Stall team. If you wanted to help the team be based around the sweep of Chandelure, Breloom or Landorus you will add things to the team that make this job easier, such as status and hazard support, putting Pokemon into OHKO range for the aforementioned sweepers. As a rater you are not looking to make the team perfect, but moreso change the team to the OP's liking.
On a different note, your layout can be somewhat hard to navigate and might make it hard for the user to see what you are trying to say. If you are simply changing a move or EV spread like you suggested for Dugtrio, there is no need to include a set, or if you do, put it in hide tags. It makes the rate a lot more compact and easier for the maker of the team to see what you are saying. The same goes for situations where you recommend a completely different Pokemon, as you don't want your amazing rate to be covered up by pictures and such. However, this is just my preference, I find that people will be more willing to accept your changes if they can read it.
This is just my opinion, don't be discouraged. Good luck rating!