In my opinion the thing about fusion events is that biggest issue isn't really having top tier champs, but rather having a lot of time and resources. In theory anyone that saves up the necessary resources should be able to clear a fusion event, even one such as the last which was arguably the most difficult of the bunch.
I have participated in a number of the events just by doing this, and I'm FTP.
Essentially this means:
Saving up all of your shards, and buying any mystery shards from the marketplace if they pop. When I saved up for Brogni I had 1600 mystery shards, 40 ancient shards, 12 void shards and 5 sacred. Just don't use them, ever. Yes, there will be a 2x Sacred event, but don't fall into that trap. If you are serious about these fusion events then you need to stockpile everything. Join a clan and start to get some chests per day, even low level ones.
Do not use Sacred shards in the champion chase tournaments, as their points are better for the summon rush ones. Infact, do not use Sacred shards anywhere if you want to. You also want to use the bare minimum shards each event, and ideally start from your lowest. Say for example you need 3000 points. 5 sacred shards = 2500 points, but if I can get away with using just 3 for 1500 points, 5 void shards for 600 points, and then 900 mystery shards for the rest, then I will do so.
Saving up energy. I am not sure what other people do but I always use the bare minimum energy per day, and stockpile the rest. With all dailies and the occasional free shop gift, you can get on average 500 energy a day. Including the weekly questions (which is 2 energy refills) and the monthly (which is 400 energy), you can get about 17,000 energy a month. I started this event at 18,000 energy, which was after saving up for 1.5 months after I had completed Astralon. I finished the event at about 8,000 energy, so I had plenty
That is pretty much it. You should get a majority of your silver (if not all) for the artifact enhancement events from the selling of gear during the dungeons and champion training events.
Ultimately it comes down to time. If you genuinely have a lot of energy in reserve, and enough shards saved up, then nothing short of time should stop you from being able to participate in these. My first fusion events were done with level 10 dungeons, and pretty much all epics/rare champions.