Koala, your personal opinion is pretty much right.
Yep, and I consider also French as one of the most difficult language, in terms of grammar, stupid rules (like plural in words after the verb to be but not for words after the verb to have, or many way to write a sound whereas it is the same like: eau, o, au which are all pronounced O, or ein, in, ain also pronounced the same way, or accents which are useless such as è or ê pronounced similarly, etc.), because you know "French has to be sophisticated"... Result of this? Most of the French youth cannot write correctly French, congrats to the French Academy!
And yeah, for people who grew up outside of an Anglophone country, pronouncing "th" is sometimes hard. Easiest way: put your tongue between your teeth, open your mouth, and make an "S" noise. It will hopefully come out as "th" if you did it right.
Yes sadly you know for a foreigner while speaking you have some "automatisms" so most of the time you do not pronounce some sounds correctly unless you work hard on your pronunciation sure.