I agree with those it’s not the “imported tag” that makes a good horse. But technically it really only means the horse has crossed a border at least once in her/his life. The reason for all the emotion is what people make of the term. It is the assumption that a horse must be particularly good because it came from somewhere else. This assumption is made in the receiving country, not the sending one. In the sending country you will find breeders ‘bragging’ about how many and where all their stock has been exported to thinking it looks good on the studfarm portfolio.
The underlying truth is that someone went to a lot of effort to locate this animal and bring it home whether it’s only a few hours across the border or across the atlantic sea.
I’ve been on both ends as my family has bred Hanoverians and our first horse that ended up being exported was born in 1980. It had sold to a jumper from the South and from there was sold on to an American who took it home when it was 9. I also buy and import Welsh Ponies from Wales to Germany on a fairly regular basis to school and use for teaching and then sell on when the right buyer comes along.
I personally find it a good idea to disclose the origin of any horse I offer for sale. It’s bits and pieces I as a buyer would want to know: Where did it come from, what has it done, what has been done with it before.
To the Welsh experts the prefix alone pretty much tells them where it came from but there aren’t only experts out there buying horses and I praise myself to provide full service incl. after sale care, plus as the breeder or trainer of the horse I have an inert interest to make sure my client buys the right horse for them and the ownership turns into a success story, not a story of failure and disappointment.
I therefor think information is a good thing so the term imported in my way of thinking is incomplete but should for the sake of information point out the country at the same time. There’s a reason why people bring horses from Canada into the States and vice versa: There are some great horses to be found in both countries.
Does the fact that a horse came from far away make it better? No. But the fact that someone spent a significant amount of time and money to take it home from god knows where and bothered to go through the paperwork-burdens with an import might very well serve as proof that they liked this animal a fair bit 
Try to look at it with less emotion and use the term as what it is, a piece of information to give to prospective buyers. Now if someone called their horse imported and it isn’t that’s a lie.
As far as Irish TB goes: If it was registered as an Irish TB it is, if it is born in the US and ‘only’ has Irish lineage it’s a TB with Irish bloodlines as far as I am concerned.