At the risk of upsetting some by sticking my nose in where it is not appreciated.
First I am sure that John knows much more than I do about siege of the stronghold and tactics to use in competitions so I wouldn't try to out do him on that.
Though I would add to your findings, and his suggestions that you probably had an unfavourable draw, and that you were not that far ahead in the categories that you were leading in, such that if you had managed to score in the category where no points were gained that your opposition couldn't have still won the match 4:3 or better, than the win on points they got from the 3:3 draw.
All this aside,I would suggest you think carefully about upgrading the stronghold to level 4, perhaps read the posts about players regretting advancing their game progresss in general, or upgrading the stronghold.
First thing I noticed was that you wrote ''I lost'' and ''My stronghold'' which made me wonder if that's what you meant,and you are a one man clan,if this is the true my suggestion about not upgrading could be more significant.
A one person clan, or even a clan with few members ,could find it more difficult to win on seige battles against a clan with more members with access to larger armies.
Also currently, not just your opponent, but any clan can attack a stronghold siege ,which is something small clans have complained about.
Whether it is just you in the clan, or many, when the draw is made you have to consider what are your chances of winning, there's not a lot of reasons for spending a lot of effort if it looks like you are outnumbered from the outset.
Maybe you do this already, maybe you win most of your matches, and this is the first time you lost a drawn match to a clan with a stronghold siege. If you upgrade to level 4 you could find that more of your opponents have siege capability, and your wins decrease in number.
Final point can you obtain enough legendary gems for the precious dust that you need?
Except I forgot to add read this Plarium post.
''Tips for activating Siege status in the Stronghold''
Here is something else I just looked at that John wrote peviously on the subject of siege and accumulating gems for precious dust.
https://plarium.com/forum/en/vikings-war-of-clans/582_general-questions/205577_help----2/
Getting this on my plate did not help me either.