Wow, you mean, even beginners can do the stuff you describe here? My personal best is still 50 m dynamic (WITH fins) after 3 years of freediving. I do have to admit that I'm only freediving now and then, but you can forget about me doing 5x50m. Or you should give me 5-6 minutes to recover after each 50m. Same goes for dive times of 1:30-2:00 while moving. I get to 1 minute and then I'm done. And as 50 m is my personal best in dynamic, you can also forget about me doing a static before it. Should I feel bad about myself now? I don't know. The thing is: I am feeling bad about myself. :-/
First of all you should never feel bad about where you are, or how long it takes to progress. Everyone is at a different level for different reasons and thats totally OK.
And yes.. the training I described is possible for relative beginners as long as they have either developed a decent base in CO2 training or are mentally tough. Unless you have a haemoglobin/ iron problem 50m DYN should never be Hypoxic and the only limiting factor at this distance would be tolerance to contractions/CO2. Horrible fining technique and posture will also increase CO2 production as well as overall stress-tension. Also, adding statics before dynamics isn't as bad as it seems, until you are reaching 1:30+ statics the actual relaxation effect of the static can actually make the DYN more comfortable, and the increased dive response that set in during the STA can counter the possibility of extra Hypoxia by reducing O2 consumption during the DYN. Its more an exercise of relaxation that it is an exercise of hypoxia as well as a simulation of Freefall+ ascent during a CWT dive.
I have no awareness of the training that you've done in the past 3 years so I cannot come to definitive conclusions but what I can say is that in almost all cases 50m DYN is initially difficult because of urge to breath, not because of low O2. If you haven't moved on from that limit it is most likely because of lack of CO2 training and not because of a breath hold limitation..
You could start off easy doing a 25m CO2 table (2:00 breathing +25m DYN, 1:45 breathing +25m DYN, reducing recovery by 15 seconds until you do 00:15 breathing +25m DYN)
When that isn't so hard do a 16x25m for time.. Its a race against the clock on this one. Try limiting to 20-25 seconds recovery for every 25m at first, and eventually get it down to 1-2 breaths recovery between each 25m.
Finally you can do the conventional Co2 table (2:00, 1:45, 1:30,... 00:15) with a 50m dynamic and then a 16x50m with 30-45 seconds recovery.
It could take a lot of mental strength to do these but its important that you do push yourself quite hard, and even if it gets uncomfortable you just keep going and work through it.. Just make sure not to over do it and fall into over training, 1-2 times per week is enough and you should see good improvements on your ability to tolerate contractions. Once you can do a 16x50, going farther than 50 with a 5 min breath up and a good warm up will be a piece of cake.