Tetsujin has summarized all of Tyrion's achievements prior to season 5, so I won't reiterate them. However, it should be noted that nearly all of Tyrion's plans and strategies from season 5 and onwards do end up succeeding.
Successes
As pointed out in the comments, Tyrion successfully managed to get both himself and Jorah to Meereen alive, then convinced Dany to make him her advisor.
Tyrion negotiated with the slavers to have a gradual phasing out period of slavery, in return for stopping their attack on Meereen. Whilst it was not ultimately successful, it did buy a reprieve from the attacking army whilst Daenarys wasn't there. This gave her time to return with Drogon and break the siege.
Once Dany had returned, the ploy to have the three masters offer one as sacrifice, leaving him alive and executing the others to ensure would be loyal sounds like something Tyrion would have thought of (I don't know if it explicitly states it was his idea, but I was under the impression that it was).
In season 7, his plan to capture Casterly Rock was successful, and Dany suffered minimal troop losses. It ended up being a trap set by Euron in order to destroy the ships that transported the unsullied, but winning control of a major castle, including all of the lands surrounding it, in exchange for half of the ships under Dany's command seems to me like a resounding success.
Tyrion advised Dany not to go north of the wall to save Jon with her dragons, which went unheeded. This led to the death of Viserion and ultimately caused the army of the dead to break through the wall. Whilst not a "success", it was a major event where Tyrion gave the correct advice.
Whilst Tyrion didn't convince Cersei to help defeat the Night King, he did convince Jaime, which lead to him revealing not only Cersei's deception, but also the fact that she was hiring the Golden Company, something that they did not know beforehand.
Tyrion told Dany that Varys had betrayed her after he learned Jon's secret. I see this as an absolute win for Tyrion, because Varys quickly turned on Danaerys when a better option came along. If Varys had found out this information independently of Tyrion, he might have been successful at poisoning her before anyone found out about it. Similar to when Tyrion rooted out Maester Pycelle as Cersei's spy in season 2, he quickly discovered that Varys was only loyal to Dany as long as it was beneficial to him and his goals.
Failures
When Jon and company followed Tyrion's plan to venture north of the wall to capture a wight to show to Cersei, they were ambushed by the Night King's army. Considering that the Night King seemingly had unexplained powers of foresight similar to Bran (he could see and touch him whilst he was warging, and he seemed to know that Daenarys was on her way with her dragons so that he could claim one and use it to break the wall) there was never any chance that they would be able to successfully pull this off.
The plan to convince Cersei of the need of an alliance against the army of the dead may have been successful, if Jon hadn't been so stubbornly honest and told her he had already pledged his troops to Dany's cause. However I believe that it's highly likely Cersei would have betrayed them anyway, so I'm still putting this as a failure for trusting her.
Tyrion convinced Danaerys to attempt to make peace with Cersei after Rhaegal's death, which led to Missandei's execution. Again he was wrong, but if they had attempted to attack directly before negotiating then Missandei would have possibly been executed anyway.
Other
After the plan to attack Casterly Rock, Danaerys lost Highgarden, Yara's fleet and the Dornish leadership. These, however, are not down to any decision Tyrion made. Despite being ambushed, the respective armies should have at least been able to reasonably defend themselves, and none of the other advisors Dany had (including Varys, Ellaria Sand, Olenna Tyrell, Jon Snow, Yara and Theon Greyjoy, Jorah Mormont and Grey Worm) expected Cersei and Euron to be so aggressive and attack where they did, so these failures don't only rest on him.
Tyrion advised Dany not to attack the baggage train as she might get killed, and she very almost did. Whilst the attack was a success for her, they don't really gain much apart from killing some Lannister troops and having some more surrender, as the gold had already been transported to King's Landing.
Dany was also ambushed when heading to Dragonstone in Season 8, and this led to the death of Rheagal and Missandei. Again, this wasn't down to Tyrion. It's unlikely that with so many battle strategists advising her, that it was solely his idea to go there without any regard for an ambush or a counterattack.
Summary
Realistically, the only time Tyrion made any mistakes with his advice was in regards to a supernatural being with some type of magical ability to know things he categorically shouldn't, and his sister. Considering that the plan to get Cersei's help originated from trying to get her to come to an arrangement with Dany, it could be argued that all of Tyrion's mistakes came from believing that Cersei was a better person than she was.
Considering that one of Tyrion's biggest issues throughout the entire series is the complicated relationship he has with his family, it's at least understandable (although not necessarily excusable, from Danaerys' point of view) that the only times he was wrong was in regards to underestimating or looking out for Cersei.
So I would say that overall, no, Tyrion is not a poor strategist. In fact, he's a fairly excellent one. His only issue seems to be his split loyalty between his family and his Queen.
It could be argued that this is exactly what makes him a poor strategist, but I would say this is exactly what makes him Tyrion.
