We did a full re-fit of our '88 boat in '21. The factory had pretty much used 5200 everywhere. I did have to use thin wedges and heat to remove a lot of deck fittings. There were a handful of places where a little bit of gel coat came up with the part, and that was before I started using a heat gun to soften it.
I found that I had almost zero water seepage around ports and tracks. However, there was evidence in several places where moisture was slowly working its way under parts and was
very close to getting inside and causing trouble. I would say, that in round numbers, about 30 years is the absolute limit for even the
best sealant to do its job. For instance, EY had countersunk all the bolt holes for the tracks to allow more sealant to bond and adhere. This increased their labor cost, but was appreciated a lot by us subsequent owners...
So, yes, the best sealants are going to be difficult to remove. They have to be to do their job. The duty of a "sealant" is to adhere stuff as well as seal it.
Aside: It also occurs to me to wonder what happened to all the boats that followed the West Systems "hardware bonding" procedure, promoted back in the 80's, to really fasten/secure heavily-loaded deck gear down. Those big turning blocks would have been bolted and epoxied in place. Wonderful in use, but removal later would be, um .... "challenging"....
BTW, having the keel and also our hull-to-deck joint so well adhered is a Really Good Thing.
(Opinions on sale for a penny, Labor Day Special !)