Yes you are completly correct there. Had the same problems. But the problem with the standard HR is, if you do interval based training like most swim teams train, that it takes the average over the whole session. The load calculation becomes terrible. A sprint interval training (for example lactate production) will have not even a third of the load of a easy recovery swim. That makes the normal calculation useless. Maybe check out the TRIMPc i made or read up on it, if you actually want to quantify by hr with interval training. It should resolve those issues, but you will have to use the manual tracking for the 100 IM’s, the drill mode or whatever it is called.
I think triathlete swimmers should be heartrate, normal swimmers pace, competitive swimmers or swimmers in a swim club will probably need to use TRIMPc. I have not found something better until now. Maybe systems like triton could do that, but that would have to be implemented on a club level.
A sidenote: The HR is not as accurate as you might think unless you are using a verity sense or hr-strap. Unless you are female, you can probalby not use an hr strap under the suit.
The arms get thrown around in swimming, the sensors already have hard times with wrist based calculations, and now we catapult blood into them every second stroke.
Hope this helps.
(Link to the TRIMPc post if you want to read up on it)